Kevin Martin Jose

Disclaimer: All I’ve done is write a few config files.

This is for you if:

1. Your python IDE of choice is PyCharm
2. You wish you had a command-line replacement for PyCharm on all the places you ssh into
3. You wish you had access to at least some of the niceties of PyCharm when editing a one-off script, without having to create/import it into a new project.
4. You are somewhat familiar with vim and can comfortably edit a single file on vim. You also know what a .vimrc is

Motivation

PyCharm has worked wonderfully well for me, and the only time where I have to use something else is when I ssh into a server to put together a quick script. That something else tends to be vim, and this is an attempt to get vim as close to PyCharm as possible – especially the shortcuts so that I can work on vim the way I work on PyCharm (well, almost). The end result is still a far cry from PyCharm, but it makes navigating a codebase over ssh significantly less painful (at least for me)

But PyCharm can work over ssh

Yeah, but I don’t use PyCharm for one-off scripts. Besides, it pleases me to know that if I can ssh into the server (from an ipad, a phone, or a washing machine), I have an (approximate) IDE I can work on.

List of working approximations

• Sorta kinda uses the same colorscheme as PyCharm
• Toggles a project navigation sidebar (NERDTree) using alt + 1 . Approximates PyCharm’s Ctrl+1
• Comment/uncomment multiple lines using Ctrl+/, just like PyCharm
• Autocomplete
• Navigate to the definition of a method/variable using Ctrl + Left click or Ctrl + b, just like PyCharm
• Jump to the previous location using Alt + - . Approximates PyCharm’s Ctrl + Alt + Left Arrow
• Fuzzy search for files using Ctrl + o. Approximates PyCharm’s double shift press
• Search the entire code base using Alt + f. Approximates PyCharm’s Ctrl + Shift + f
• Edits made in the search results window are reflected on to the underlying file, just like PyCharm
• Syntax and linter errors show up as you type, just like PyCharm
• If you are editing files that are part of a git repository, there are indicators on the gutter to show added, modified and subtracted lines, just like PyCharm
• Pressing F12 brings up a terminal. Approximates PyCharm’s Alt + F12
• Code folding using the minus (i.e -) key. Approximates PyCharm’s Ctrl+- and Ctrl + +
• Automatic file saves, just like PyCharm
• Rename methods/variables and automatically fix imports e.t.c across files, just like PyCharm

Why not just use python-mode?

I simply could not figure out the shortcuts that python-mode used. I thought it would be easier and more flexible if I install and configure the plugins myself.

Prerequisites

• vim 8
• A Python virtualenv (or a conda environment). There’s some pip install involved, though this is optional
• Patience

TL;DR

Go here for the .vimrc

Let’s start from a blank .vimrc

If you need a project-specific .vimrc, see this. If not, everything goes into your ~/.vimrc

Let us begin by being able to see line numbers and some sort of syntax highlighting everywhere. Put these on your .vimrc:

" Some basic stuff
set number
set showmatch
syntax on
imap jj <Esc>

The set showmatch is for highlighting matching parentheses – that’s useful. The last line maps double pressing the j key in insert mode to <Esc> – no more reaching for that far away Escape key using your pinky!

NERDTree for the sidebar

We’ll start our plugin-hoarding with NERDTree. With Vim 8, we can simply copy over a plugin directory to a certain place and Vim would just “pick it up” – there’s no need to use a plugin manager for achieving VimCharm. Create the necessary directory structure and clone NERDTree:

mkdir ~/.vim/pack/vimcharm/start/ -p
git clone https://github.com/preservim/nerdtree.git ~/.vim/pack/vimcharm/start/nerdtree

Open some file (any file) on vim and type :NERDTreeToggle – you should see the sidebar. Executing the same command again would close the NERDTree. PyCharm by default opens/closes the sidebar using Ctrl + 1 . However, the terminal (and consequently Vim) cannot differentiate between 1 and Ctrl + 1, so we’ll map this to Alt + 1 instead. Before we do that, we need to determine what characters are sent by the terminal when we press the key combo. Simply run cat without any arguments, and press Alt + 1. You should see something like this:

You would also see that 1 and Ctrl+1 produces the same character on cat – as far as I know, there’s no way around this.

We need to map the character sequence for Alt + 1 to :NERDTreeToggle on our .vimrc:

set <A-1>=^[1
nmap <A-1> :NERDTreeToggle<CR>

Take care not to simply copy paste the character sequence on to your .vimrc! That won’t work. You should open your .vimrc on Vim, go to insert mode, and press Ctrl+v – this would put a caret under your cursor – now press Alt + 1 and it should fill in the necessary characters there. Restart vim, and Alt+1 should now open and close NERDTree.

Making it look like PyCharm

Gruvbox looks like the default PyCharm theme, kinda, so let’s get that:

git clone https://github.com/morhetz/gruvbox.git ~/.vim/pack/vimcharm/start/gruvbox

According to the installation page, we need to add this to our .vimrc:

autocmd vimenter * ++nested colorscheme gruvbox

Commenting and Uncommenting lines using Ctrl + /

We are going to use NERDCommenter for this. Clone it into the right directory, just as before:

 git clone https://github.com/preservim/nerdcommenter ~/.vim/pack/vimcharm/start/nerdcommenter

Ctrl+/ cannot be directly mapped on your .vimrc. So just like before, we insert the correct escaped character sequence into our .vimrc by going into insert mode, pressing Ctrl+v, and then pressing the desired keycombo (Ctrl + / in this case).

" The part after "=" in the below line should be inserted using Ctrl+v while in insert mode and then pressing Ctrl+/
set <F13>=^_
noremap <F13> :call NERDComment(0,"toggle")<CR>

" So that NERDCommenter can automatically decide how to comment a particular filetype
filetype plugin on

We are telling Vim to map the character sequences that Ctrl + / produces to the F13 key, which probably does not exist on your keyboard, and then we map F13 to the appropriate command to toggle comments. Restart Vim, open (or create) a python file and try Ctrl + / while in normal mode – it should comment/uncomment the line.

Autocomplete

Autocomplete on Vim does not feel as “fluid” as on PyCharm – for example, I haven’t managed to get it to work on imports – but it is still besser als nichts. Get jedi-vim:

 git clone https://github.com/davidhalter/jedi-vim ~/.vim/pack/vimcharm/start/jedi-vim

Restart vim, and Ctrl + space should already be giving you autocomplete suggestions. IMHO, jedi-vim displays too much information (what even is that bar thing that comes up on top?) – all I wanted was a simple autocomplete prompt. Put this on your .vimrc to Make Autocomplete Great Again:

let jedi#show_call_signatures = 0
let jedi#documentation_command = ""
autocmd FileType python setlocal completeopt-=preview

EDIT: I also installed supertab along with jedi:

 git clone https://github.com/ervandew/supertab ~/.vim/pack/vimcharm/start/supertab

Go-to definition using Ctrl+click

This is something that jedi-vim already does – all we need are some .vimrc entries:

set mouse=a
let g:jedi#goto_command = "<C-LeftMouse>"
map <C-b> <C-LeftMouse>

The above lines enable mouse support on Vim, sets Ctrl + left click as the combination for jedi’s goto command, and then recursively maps Ctrl+b (which is also what PyCharm uses by default) to Ctrl + left click as a keyboard-friendly alternative.

I also prefer the goto command to open a new tab when navigating to a different file. Here’s how to enable that, along with Shift+j and Shift+k to move between tabs:

let g:jedi#use_tabs_not_buffers = 1
nnoremap J :tabp<CR>
nnoremap K :tabn<CR>

Jump to previous location using Alt + minus

If you end up navigating multiple tabs away using Ctrl+b, you can press Ctrl+o repeatedly to jump back to your original position. Press Ctrl+i to go in the other direction. These would come in handy if you have to quickly gg to the beginning of the file to add an import – you can then press Ctrl+o to go back to the line you were editing. I believe in PyCharm the default mappings for this are Ctrl + Alt + Left arrow and Ctrl + Alt + right arrow respectively. I remapped these to Alt + - and Alt + Shift + - (that would be in fact Alt + _ ):

set <A-->=^[-
noremap <A--> <C-O>
set <A-_>=^[_
noremap <A-_> <C-I>

Remember that copy-pasting these won’t work and you will have to enter insert mode and press Ctrl+v and then Alt + -

Fuzzy file search

Fuzzy file search is what PyCharm does when you press the Shift key twice.

Download CtrlP:

git clone https://github.com/kien/ctrlp.vim.git ~/.vim/pack/vimcharm/start/ctrlp

By default pressing Ctrl+p should bring up the search prompt. We can’t map this to double shift (as in PyCharm) since vim can’t recognize Shift key presses (unless it’s combined with a printable character). I decided to map this to Ctrl + o instead (“o” for open), though this is not any better than the default setting. On your .vimrc:

let g:ctrlp_map='<C-O>'
let g:ctrlp_cmd='CtrlPMixed'

The second line above specifies that the search should be over files, buffers, tags e.t.c – you may omit it if you do not want buffers to show up on your search. ctrl+t on a search result will open it in a new tab.

Search everywhere and replace

One of the most useful features in PyCharm is the “search in project” dialog that Ctrl + Shift + f brings up. For example, if I delete/rename a hard-coded string literal, this is the dialog that I would bring up to look for all occurrences of that string literal so that I can rename/delete all of them – right from the search window.

Instead of using the built-in vimgrep or making an external call to the ubiquitous grep, we are going to use ack because it excludes annoying things like gitignore and binaries from the search results by default.

1. Somehow get ack on your target system
2. git clone ack.vim to ~/.vim/pack/vimcharm/start/ack.vim

We are going to map Alt + F to a python-only smart-cased search with ack. Add these to your .vimrc:

set <A-F>=^[f
nnoremap <A-F> :Ack! -S --python 

Remember to Ctr+v and then press Alt+F to get those escaped character sequence right. Also, there is an extra space after the --python. Without it, the search term (eg: “foo”) that you type after pressing Alt+F would end up being “–pythonfoo”.

Restart vim and press Alt+f in a python file, enter your search term, and press enter. The results will be shown in a quick-fix window. Move your cursor to a search result and press enter to jump to that location. Press t to open that location in a new tab. Either of these would shift the focus to the editor. Press ctrl + w twice to shift focus back to the quick-fix window.

I usually use /<pattern> to search within the file, but sometimes it’s useful to do a slightly fancier search. I’ve wired Ctrl+f (the regular PyCharm find-in-this-file) to do a search within the open file:

nnoremap <C-F> :Ack!  %<Left><Left>

By default, you cannot make any changes to the contents of the quick-fix window. In Pycharm, the search results are editable and the changes are reflected on the underlying file. We can pull this off using the quickfix-reflector:

git clone https://github.com/stefandtw/quickfix-reflector.vim.git ~/.vim/pack/vimcharm/start/quickfix-reflector.vim

That’s it! Now your edits on the search results should be reflected on the underlying files.

Spot syntax and linter errors as you type

The most annoying thing about writing Python on Vim, at least for me, was that the silly syntax errors I make won’t be discovered until I actually try to run my script – PyCharm usually catches these as you type. Let’s set this up on vim using ALE:

git clone https://github.com/dense-analysis/ale.git ~/.vim/pack/vimcharm/start/ale

You should also have a linter insalled. I use pylint, and a quick pip install pylint does the trick. Restart vim and open a python file, and it should already be linting it as you type. Since ALE works asynchronously, there will be a slight delay (around a second) between you making a mistake and it being flagged on Vim – but in my opinion this is much better than a synchronous linting which freezes Vim, which is why I chose ALE instead of syntastic. However, the default ALE + Pylint combo is too whiny for my taste – I don’t want warnings about how I’m not writing a docstring for every single method; I have this on my .pylintrc:

[MESSAGES CONTROL]
disable=trailing-whitespace,missing-function-docstring,missing-module-docstring,no-else-return,miss    ing-class-docstring,invalid-name

The above is far from how I would like linter to be configured, but it serves as an initial config. I also do not care for highlighting the offending word in a line – all I want is a non-invasive indication in the gutter. On your .vimrc:

let g:ale_set_highlights = 0

Show lines modified after the previous commit

Put vim-gutter at ~/.vim/pack/vimcharm/start/vim-gutter and restart vim. If you edit a file in a repo (or set up git on your current folder with git init), the modified lines would be marked in the gutter. By default it takes 4 seconds for the appropriate mark to appear on your gutter – let us reduce it by putting this line in the .vimrc:

set updatetime=100

The end result is rather unflattering. ALE and git-gutter does not work well together – git-gutter’s modification marks are drawn over by the linter warnings, and in some-cases ALE ends up marking the wrong line with a warning. This thread suggests that there’s probably a way to get them to work the way I want, but I haven’t invested much time here.

Have a terminal handy

In Vim :term will open a terminal in a split window. Mapping this to F12 is trivial, but we want to hide this terminal (instead of killing it) and bring it back again on pressing F12. I could not get the “hide terminal on F12” part working, but I did figure out how to bring up a hidden terminal if it exists (or create a new terminal if it doesn’t) on pressing F12. Before we write a script for it, let’s go through the motions manually:

1. Open Vim
2. Type :term to open a terminal in a split window
3. Type something on the terminal
4. Press Ctrl+w and then type :hide to hide our terminal window
5. To show our hidden terminal, type :sbuffer /bin/bash. This would open in a split window a buffer that has “/bin/bash” in its name. If you use something other than bash, you will have to change this string accordingly.

Here’s a LoadTerminal() Vim script I wrote that would bring up an existing bash buffer if it exists, or create a new one if it doesn’t:

function! LoadTerminal()
    let bnr = bufnr('!/bin/bash')
    if bnr > 0 
        :sbuffer !/bin/bash
    else
        :term
    endif
endfunction

Save it as load_terminal.vim at ~/.vim/pack/vimcharm/start and add the following lines to your .vimrc:

source ~/.vim/pack/vimcharm/start/load_terminal.vim
map <F12> :call LoadTerminal()<CR>

The annoying part here is that we can’t map key presses on the terminal window – so you’ll have to press Ctrl + w and type :hide to hide the terminal. Do let me know if you find a way to map this to a keystroke.

Code folding

When you deal with large files, code folding (those tiny “-” signs that you click on PyCharm to collapse an entire class/method) is a godsend. Fortunately vim supports code folding right out of the box and all we need is this on our .vimrc:

set foldmethod=indent
set foldlevelstart=99
nnoremap - za
map _ zM
map + zR 
        

According to our mappings above, there are no folds (i.e every code block is “open”) when we open a file (this is what foldlevelstart specifies). Shift + - (i.e Shift and the minus key) will collapse all blocks, and Shift + + will open all blocks. Use the minus key (i.e -) to toggle collapsing a single fold. You might also want to check out this answer for a quick overview of what’s supported.

Auto save

PyCharm saves the file as you type, sparing you from the hassle of having to press Ctrl+S across multiple tabs. We can get Vim to do this with vim-auto-save. Clone the repo to ~/.vim/pack/vimcharm/start/vim-autosave and add these to your .vimrc to enable auto-save:

let g:auto_save = 1                                                                                
let g:auto_save_events = ["InsertLeave", "TextChanged"] 

A word of caution before we proceed – auto-saving can get quite annoying if enabled globally. I use project-specific vimrcs and use auto-save along with git – so if I accidentally auto-save something that I shouldn’t have, a git diff is all I need to see what went wrong.

Refactor across files

Jedi-vim can do simple renaming, but I wanted to something more powerful. Enter ropevim. You need to pip install rope, ropemode and ropevim. I have a miniconda environment set up, but you can install the packages to your global scope if you want to. We just need one file from the ropevim repo:

wget -O ~/.vim/pack/vimcharm/start/python_ropevim.vim https://raw.githubusercontent.com/python-rope/ropevim/master/ftplugin/python_ropevim.vim

Now let’s source it in our .vimrc:

 source ~/.vim/pack/vimcharm/start/python_ropevim.vim

Now add these to your .vimrc:

nnoremap <C-z> :RopeUndo<CR>                                                                       
set <A-z>=^[z                                                                                      
map <A-z> :RopeRedo<CR>                                                                            
map <F6> :RopeRename<CR>

We have mapped F6 to the rename operation, and Ctrl+z and Alt + z to undo and redo respectively. Remember not to copy paste the mapping for Alt + z, and press Ctrl+v and then the desired keycombo to enter it in your .vimrc.

Restart Vim, open a python file, and try to rename a variable using F6. You will get prompts to create a new ropevim project – press ‘y’ to create one locally, and then proceed to apply the rename. If you get an import error for ropevim when you start Vim, it’s probably because Vim uses the system python (which is probably a different version than the python in your virtualenv) and you pip-installed rope, ropemode and ropevim to a virtualenv. An alternative would be to do conda install -c conda-forge vim on your anaconda/miniconda env so that the Vim in your env will use the local python (and hence your installed pip packages) instead of the system one.

Final thoughts

If anything this exercise has made be better appreciate the work that the Jetbrains devs have put into their IDEs – all I wanted was a working subset of PyCharm’s basic features and what I got was a rather modest approximation. Do let me know (open an issue on Github?) if you managed to get any closer to PyCharm than this.

As originally published in Squad Engineering

Disclaimer: Though this post sounds like fancy startup propaganda, it is not. I still stand by what I’ve written, even though I no longer work at Squad.

Considering that the Joel test dates back to the turn of the century, a time when Pentium III was state of the art and Linux was still obscure, it has aged quite gracefully. It is no more the golden standard against which development teams are rated, but it still is surprisingly relevant (for the most part).

At Squad we strive to build an engineering culture of doing more with less, and having a super smooth kick-ass development workflow is a necessity, not a luxury. Here we go.

1. Do you use source control?

Yes, git. All our code lives on Github. This one’s a no-brainer.

2. Can you make a build in one step?

One step builds are nice, but no builds are even nicer. In python-land, you don’t build — you deploy. As a developer, all I have to do is commit my changes to the staging branch, and do a fab deploy and voila! I can now test my changes on our staging server to my heart’s content . The whole deploy to staging process takes less than 5 minutes. Deploying to production is just another 5 minutes away, assuming you tested your feature on the staging server thoroughly.

3. Do you make daily builds?

As I said, we don’t really have ‘builds’ and that’s a good thing. What we do have is continuous integration using CircleCI. Unit tests are run automatically every time I commit to the repo and with a Slack integration, the team gets notified whenever a build is completed.

4. Do you have a bug database?

Yes, we track all our features and bugs on Pivotal Tracker. We have git integrations and every commit to the repo is automatically recorded under the relevant story. All discussions relevant to a bug/story happens at a single place. Did I mention we seldom use emails? Yup, that’s right, I can count on my fingers the number of times I had to use email for communicating with my teammates.

5. Do you fix bugs before writing new code?

Depends. Before you go berserk thinking “Why would Squad dooo thaaat?” let me humbly point you to Jeff Atwood’s take on the matter — not all bugs are worth fixing. Since we strive to be as lean as possible, every hour we sink into a bug has to be justified. In fact, our developers ruthlessly confirm the ‘ROI’ first before diving into the code base to hunt down and fix the bug.

That being said, you’ll never see a Squad dev building a feature on top of an existing bug. If thou see-eth the bug, thou fixeth the bug while writing thy feature. Also we don’t believe in titles, so the decision to whether fix a bug or not usually comes down to you and not to a mystical manager two tiers above you.

6. Do you have an up-to-date schedule?

We have ‘solver teams’ that are super committed to solving a focused problem and each solver team has a set of Objectives and Key Results (OKRs) for a quarter. This results in a very transparent schedule, agreed on by the whole team, and meeting or breaking it (if necessary) is always a collective decision and not a directive from up top.

What this means is that if Squad was trying to colonize Mars, every member of the solver team would know exactly when to work on making the landing lights look nice and when to focus on just hurtling the shuttle in the approximate direction of Mars.

But despite our best efforts, sometimes deadlines are missed. We try to shed more weight (no landing lights on the rocket) and invoke ** ‘focus on focus’ to get the most critical components shipped. What happens if we’re still unable to meet the schedule? That’s when we own up that our estimates were incorrect and do it better the next time.

** Focus solely on what is worth focusing on. Thanks, Rishabh

7. Do you have a spec?

Walking on water and developing software from a specification are easy if both are frozen — Edward V. Berard>

Remember what I said about stories in Pivotal Tracker? Our specs too live inside stories. This is the process we follow:

• Discuss with all stakeholders and draft a requirements doc. This doc will act as the source of truth for what needs to be solved and what needs to be built. This is our spec, and it is frozen as far as this story is concerned
• Design a solution. What’s the easiest, most elegant way to meet the specs? Write down the design, the tasks involved and estimate the story
• A teammate reviews your design, and a meaningful discussion about the merits of your design and alternate solutions ensue
• You and your reviewer agree on a design, and you happily code away

8. Do programmers have quiet working conditions?

Oh this is my favorite part.

We have two really cool ‘silent rooms’ anybody can go to when they feel that the office bullpen is getting too loud. Once inside, you are not allowed to talk (unless you and your buddy have super-human whispering skills) and your phones should be on silent. Not on vibrate, but on silent. This is the metaphorical cave where programmers disappear into and come out with bags full of features. Silent rooms are our rock and our refuge, the one place where we won’t be disturbed. The rooms are insulated so that if someone revs their bike right outside the window, we wouldn’t know about it. And yes, I’m writing this blog sitting in one of the silent rooms.

9. Do you use the best tools money can buy?

Yes, developers bring their own device to work. I actually moved my assembled desktop into the office since I was convinced that an underpowered laptop without a discrete GPU won’t be able to ‘handle me’. Whatever makes you productive.

IDEs too are up to you to decide, and my favorite contester is PyCharm. We also have employed a slew of awesome tools like Slack, Sentry, and Loggly to make sure that our developers are as productive as they can be. Look at our StackShare page for more.

However, this does not mean we have a paid subscription for insert your favorite tool for x here. We don’t give MacBook Pros to our developers (but we do finance interest-free EMIs if they choose to buy one). We just recently got Slack premium. We are moving from Asana to Clickup. We have not maxed out the parallelism of our CircleCI builds. We also don’t swim in money. We only buy things that make us more productive.

10. Do you have testers?

No. The developers are responsible for their stories/features and they are expected to test it well before pushing to production. However, since another pair of eyes is always better, the person who requested the story (usually a Product Manager from the team) would do an ‘Acceptance Testing’ to make sure what you wrote conforms to the (hopefully frozen, rock solid) specs.

11. Do new candidates write code during their interview?

Yes, an insane amount of code. These are the steps that you would go through to get hired as a Product Engineer at Squad:

• A call from our awesome CTO, Vikas
• A design round, over the phone
• A take-home assignment. (During my interview, I spent around 2 days on it and wrote a lot of code)
• The team at Squad runs your code, and see if it works as intended. Bonus points if you have a readme.md that makes our life easier
• The team then reviews your code. I want to stress this part. We actually read your code, and it ‘works’ does not mean you pass
• A meaningful discussion over email about your chosen design and execution
• You get invited for an on-premise interview. First round is ‘activity extension’ — extend your take-home assignment to add a couple of features. If your methods/modules were too tightly coupled and inflexible, you’d have a hard time here
• Another design round. You are expected to design the solution to a problem, and write skeleton code to solve it. Given the time constraint, you get bonus points if your code actually works
• A bug smash round. You are given a code base and your task is to refactor it according to your definition of ‘good code’

Yes, that’s a lot of code and I guarantee you that it will be the best technical interview you’ve ever had!

12. Do you do hallway usability testing?

Remember what I said about our high octane HQ? It is almost impossible to keep a feature under the wraps till the time it’s released. “Oh Kevin it looks cool but I don’t think it is really useful because of x and y” happens a lot and I’m grateful for it. Continuous improvement and constant iteration is part of our DNA. That being said, there has also been instances where I waited too long to show my features, or I committed to production and then asked the stakeholder to go through the feature. Hallway testing is a guideline. Though we strive to follow the best practices and guidelines whenever possible, it is not always possible. As they say, it is easier to ask forgiveness than to ask for permission. Not always, but sometimes.

So we’re finally here — time to count the points. I would claim that we scored a solid 11, but a skeptic would argue that we barely made a 10. You be the judge.

Also there are a lot of questions that the test does not address, like how easy it is for developers to work remotely (very easy, our team is partly remote) and how often do you refactor code (very often). But I’ll defer that to another post.

Image courtesies:

• Hand holding the medal
• The cool space collage

This post was much ‘shittier’ than it is now. Thanks to my wonderful friends at Squad for helping me fix it

After 2 years at an enterprise backup software firm, I finally took the plunge and joined a startup. I love the engineering culture we have here at Squad, and rigorous code reviews are very much a part of it. Since I often found myself repeating the same mistakes again (and again, and again..), I went ahead and wrote a checklist to help me.

This is not a generic list and is very much tied to me and the mistakes that I made. The list helped me, but your mileage may vary

The TL;DR

Read through the code you wrote, and stop and ponder at each line.

The actual (noobie) list

1. No create/update inside a loop

Are you making create() or update() calls in a loop? Have you considered whether they could be replaced with bulk_create() and bulk_update()? See the django-bulk-update package.

2. No unnecessary model attribute fetches

Are you writing post.id where you could have gotten away with post_id? For example:

class Blog(models.Model):
     title = models.CharField(max_length=200)


 class Post(models.Model):
     blog = models.ForeignKey(Blog)
     time = models.TimeField()
     author = models.CharField(max_length=100

Let’s say you want to know the id of the blog to which a particular post belongs to. One way is to do:

 post = # some how get a reference to a Post object
 print post.blog.id

But the better way is to do:

 print post.blog_id

What’s the difference? In the first case, we are asking Django to fetch the id attribute from the post’s blog entry. As you would probably know, Post and Blog are separate tables in the database. So when you ask for post.blog.id, Django will query the Blog table to fetch the id that we need. That’s an extra query. However, this is not really necessary because we have the information we need in the Postobject itself. Since we have a foreign key relationship from Post to Blog, django must somehow keep track of which post is related to which blog. Django does this by storing a special blog_id attribute in Post which would store the primary key of its parent Blog. So post.blog_id would give us the information we need, without resulting in an extra query.

3. Docstrings and comments are important

Read through the docstrings and comments. It might seem unimportant to read the docstrings and comments when you have a feature to ship. But a wrong comment/docstring can throw the next developer who reads your code off track, and trust me you don’t want to be that guy.

4. If possible, limit your business logic to the model classes

Be mindful of where you write your business logic. Coming from jquery world, I had a tendency to put my business logic wherever I please. Avoid writing business logic in ModelAdmin classes or ModelForm classes (yikes!) and write them where they belong – Modelclasses. This would ensure:

• Consistency in the codebase. If it is business logic, there’s only one place it could be.
• Better tests. If it’s in a Model class, then you know you should write unit tests for it

5. Is it covered by unit tests?

Speaking of unit tests, how do you decide when to write unit tests and when not to? If it’s business logic, it needs unit tests. No buts, no maybes, just write the damn tests. If it is something in your ModelAdmin, then you can afford not to write unit tests for that as long as you don’t do any fancy if..elses there. Test your business logic, not your boilerplate

6. Think how your changes affect the existing data

In some cases, for example, when you introduce a new field, you might have to write a data migration so that existing rows in the table would have a sane value for that field. I made the rookie mistake of happily coding away on my feature with nary a thought about the existing data in the database and regretted it afterward. See here for a primer on Django migrations

7. Use that cache!

Keep an eye out for things that can be cached. Find yourselves fetching ‘top 10 scorers of all time’ from the db everytime the page loads? Cache it! Though this should be fairly obvious, it’s easy to forget about the cache when you are busy writing your feature.

8. Offload non-critical heavy tasks to an async queue

Okay, this one is a little specific to our particular stack. Let’s say you have a feature where your user presses ‘generate cats report’ button and you wade through the entire database to figure out how much of your total traffic involved pictures of grumpy cats. It is probably not a good idea to make your user stare at a loading screen while we crunch gigabytes of cat data. Here’s what you could have done:

• When the user presses the button, start an async task to calculate grumpy cat traffic volume. We use celery to make this happen.
• Once you fire the async task, immediately respond to the http request with the message “Looking for grumpy cats in the system, we will let you know when we are done”. Now your user can use his/her time for something more productive
• Message the user in slack/send an email/display a button on the page when your async task is done.

This will let us offload heavier tasks to spare EC2 instances so that more critical requests/queries do not get slower because of grumpy cats

9. Be aware of popular optimizations

Know your python. Use list comprehensions over for loops, izip over zip, et cetera. This comes with time and practice, so don’t sweat it. Oh and don’t forget this:

need_refuel = None
if fuel_level < 0.2:
    need_refuel = True
else
    need_refuel = False

The above mess can be refactored into:

need_refuel = fuel_level < THRESHOLD or False

Whether this aids or impairs readability is a whole different debate. Things like these are subjective, and it is okay to have opinions.

10. Query only what you need

If you had a model like this:

class Banana(models.Model):
    gorilla = models.CharField()
    tree = models.CharField()	
    jungle = models.CharField()

(God save you if you actually have a class structure like that in production, but it would serve our example well) And you want to do something like this:

banana = Banana.objects.get(id=3)

What you wanted was a banana, but what you got was a gorilla holding the banana with the tree it was sitting on along with the entire fricking jungle (thanks, Joe Armstrong for the quote). Not cool.

What you can do instead is:

banana = Banana.objects.get(id=3).only('id')

Here’s the documentation for only. No more gorillas, just the banana. However, I prefer using .value_list('id', flat=True) over only('id') because the latter might result in extra queries if we carelessly try to use any attribute other than id in our code. Using .values() is very explicit and conveys to the programmer that you only need this particular attribute here. It is also faster.

11. Learn to use Django Debug Tools

Django debug tools is your friend. Lavishly using only() and defer()could bite you back if not careful. If you defer loading attributes that you don’t think you will need, but you end up needing them anyways, that would be an extra DB query. At least in the Django list pages, this would result in the dreaded n+1 query. Let’s say you want to tabulate bananas and gorillas:

You thought all you need is id and Gorilla, so you did Banana.objects.all().only('id', 'gorilla'), so that we don’t need the tree and the jungle. But 3 months later, you thought it would be a good idea to display where the gorilla came from in your table. So you fire up a custom function in the ModelAdmin to do this:

def gorilla_details(self, obj)
    return '{0} {1}'.format(obj.gorilla, obj.jungle)

And everything worked smooth. But unbeknownst to you, Django is making DB queries in a loop. We had told Django to get only id and gorilla through the only() method. We now need the jungle as well. So whenever we access obj.jungle, Django queries the DB to get the jungle because we specifically told it not to fetch the jungle earlier. So we end up making 10 calls to the db for 10 gorillas (or bananas, whatever). The fix is to include jungle in the only() clause, but more often than not we do not even know that we are making an n+1 query.

Enter django debug tools.

Among many other things, DDT will tell you how many queries were fire to load your page. So if our banana-gorilla table makes 35 queries to the database to load, we know something’s wrong. Always look at what the debug toolbar has to say before you send in that pull request for review

Sorry for the long post. Here’s a potato.

This article is inspired by the excellent tutorial by Scott Luptowski on how to add authentication to you React app. I attempt to re-invent the wheel again because the original article cites an older version of react-router and the instructions do not work if you are using react-router 4.x. There are a lot of breaking changes when you migrate from 3.x to 4.x, and there is an answer to all the whys here

Disclaimer

I’m not a Reactjs ninja or rockstar or paladin or anything of that sort. Just a dude with good intentions who had to spend an entire evening trying to figure out how authentication with react-router 4.x works, when the internet had only tutorials that use 3.x. So take my advice with a pinch of salt – I might not be following the best practices.

The goal

Your glorious new app requires the user to log in before they are allowed to do certain things. For example, if you were building the next Twitter, your users shouldn’t be able to tweet unless they are logged in. The idea here is to put certain URL patterns/pages behind an authentication wall so that if a user visits that page and the user is not logged in, he/she should be redirected to a login page. If the user is already logged in, proceed to show the requested content – and the user will have no idea about the karate chops we did behind the stage. Should the user try to navigate to a page that does not exist, we should show a 404 component as well.

The how-to

The solution is simple enough. Just like Scott explained in the original article, we create a React component that contains the login logic. This component wraps all of the routes that require authenticated users. Our entry point to the app would look something like this:

ReactDOM.render(
  <Router>
	<App />
  </Router>,
  document.getElementById('app')
);

But where did all the routes go? From react-router 4.x, you don’t get to define all your routes in one place. Yep, you read that right. So our Appcomponent will be doing its part in routing:

<pre class="wp-block-syntaxhighlighter-code brush: jscript; notranslate">class App extends Component {
	constructor(props){
		super(props);
	}

	render() {
		return (
			<div>
				All the awesomeness in the world converged to a single component.
				
					
  					
  				
			</div>
		
		)
	}
}</pre>

So what are we doing here? If the url exactly matches /, we render a Homecomponent. For everything else that is a subset of /, we render RootRouteWrapper which will subsequently route our requests. So all the other url patterns (eg: /pizza, /pizza/yummy) would go on to render the RootRouteWrapper component. But what’s that Switch component doing there? If we had not enclosed the routes in a Switch, react-router would have rendered all routes that matched the url. So if the user visits your-awesome-app.com, all the routes for / will trigger – both Home and RootRouteWrapper! If your routes are enclosed in Switch, react-router will render only the first match – in our example the Home component.

OK. So now we can show a home page. What does the RootRouteWrappercomponent do again?

<pre class="wp-block-syntaxhighlighter-code brush: jscript; notranslate">class RootRouteWrapper extends Component {
	render() {
		return (
			<div id="RootRouteWrapper">
				
					
					
					
				
			</div>
		)
	}
}</pre>

We define 2 routes here – /login to show the user a login prompt and /tweet to let the user post a tweet. Now /tweet should be accessible only if the user is logged in. EnsureLoggedInContainer is the magic component that will handle the login logic for us. The idea is to configure all routes that need authentication to render the EnsureLoggedInContainer. You can also see that we have defined a route that will render the PageNotFoundcomponent if the URL does not match any configured routes. On to our login logic:

import {Route, Switch, withRouter} from 'react-router-dom';

class EnsureLoggedInContainer extends Component {
	constructor(props){
		super(props);
	}

	componentDidMount(){
		const {dispatch, currentURL, isLoggedIn} = this.props;

		if(!isLoggedIn){
			this.props.history.replace('/login');
		}
	}

	render() {
		const {isLoggedIn} = this.props;

		return (
			<Switch>
				<Route path="/tweet" component={Tweet} />
			</Switch>
		)

	}
}


export default withRouter(EnsureLoggedInContainer);

The assumption is that the Tweet component shows the user an input box to type a message. Notice how we have declared a Route for /tweet again inside the EnsureLoggedInContainer. When the user navigates to /tweet, RootRouteWrapper renders EnsureLoggedInContainer which in turn renders Tweet. If the user is not logged in, componentDidMount will redirect the user to the login page. Remember that you need to export the class with withRouter for the history to be available in the props. Also, you would need to maintain the state of the application separately – this article assumes that you have laid down the necessary plumbing to pass isLoggedIn as a prop to EnsureLoggedInContainer. isLoggedIn should come from your application state – and react-redux seems to be the most popular choice here. How to use react-redux to pass properties to your component is beyond the scope of this article. If you are interested, there’s a really good introduction here

In case you wanted to add another page that displays a tweet – say /tweet/1– that would show the tweet with id 1 in a TweetContainercomponent – you would have to write the necessary routing logic inside the Tweet component. /tweet/:id would automatically require authentication since its parent route – /tweet – renders EnsureLoggedInContainer.

Caveats

You have to make changes at 2 places to add a new route that needs authentication – in the RootRouteWrapper component and then again in EnsureLoggedInContainer. I wonder if there is a more elegant solution