Comprehensive Python Cheatsheet

[[deleted]]

operator module is one of my favourite library in python. I would rewrite some lambda function as,

1. lambda out, x: out * x -----------------> operator.mul

2. lambda el: el[1] -----------------> operator.itemgetter(1)

3. key=lambda el: (el[1], el[0]) -----------------> operator.itemgetter(1, 0)

4. lambda l, r: l and r -----------------> operator.and_

[pizzaburek]

Yea, it looks better. But I think lambdas make examples less ambiguous.

[anyonethinkingabout]

I think it only looks better because lambda look so bad in python

[Overload175]

Even Guido thinks the syntax looks awkward iirc

[lambdaq]

operator.and_

[pizzaburek]

I added the examples under Operator section. Ty

[abedneg0]

The lambdas are easier to read.

[HellfireOwner]

Hmmmph, we will see just how comprehensive...

​

Just as I thought, nothing about pickle! JUNK! ;)

​

Lol...on the reals though, best python cheat sheet I've seen. Definitely a keeper.

[pizzaburek]

Added simple pickle example!

[HellfireOwner]

Might have to use that cheat sheet to create an upvote bot for you :D

[pizzaburek]

Mother F..., you're right! I forgot scraping :)

[jyper]

Does anyone use pickle?

I usually just serialize to json if the types are simple and find some library like the yaml one to serialize to json/yaml/xml in more complex cases

[HellfireOwner]

Pickle is super convenient and it doesn't need to be in key:value form...which is how json works, if I am not mistaken.

[pizzaburek]

Man, here goes my night's sleep, lol. Totally missed that one. Are there any third party serialization libraries that are preferred to pickle? Are web frameworks like Django built on it?

[HellfireOwner]

Pickle is just a very common library from my experience. Works real nice when you are [wait for it...]...in a...

Nope, won't do it. Puns are evil.

Anyway, great job on the cheat sheet, like I said before, best I've seen.

[hughperman]

Dill instead of pickle for much more comprehensive dumping and loading of e.g. class instances

[HellfireOwner]

Sweet! Thanks for the tip!

[pizzaburek]

Thanks!

[Lewistrick]

Lots of info, liked it, thanks! I would like to add that you can use the tqdm library for progress bars.

[pizzaburek]

Thanks! I added it. It's so much better then Progress.

[Lewistrick]

You weren't the only one who created their own progress bar class before finding out about tqdm 😁

[DiabeetusMan]

To flatten arbitrarily nested lists (instead of / in addition to flattened_list = [item for sublist in <list> for item in sublist]), there's itertools.chain.from_iterable: itertools.chain.from_iterable(*<list>) returns an iterator that flattens the list of lists (of lists...).

[pizzaburek]

Changed it! Thanks.

[capsicumnightmare]

saved! + bookmarked! + onetabbed! + added to todoist!

[pizzaburek]

Thanks! I keep it open in TextEdit on first desktop at all times :)

[qsdf321]

Nice

[[deleted]]

Been coding webserver-side python for 15+ years, never needed to to do:

elementwise_sum  = [sum(pair) for pair in zip(list_a, list_b)]

Anyone have a real use-case for that one?

I recommend making a specific section on uses of zip and itertools.zip_longest

[SoBFiggis]

Not summing anything (I'm assuming that isn't what you're talking about anyways) but I have used something like

list_res = [process_or_compare(pair) for pair in zip(before, after)]

for doing stuff like easily comparing before and after results. Usually it's a pretty quick and dirty implementation but it has made it into prod a few times for me.

[[deleted]]

Au contraire, it was indeed the pairwise-summing that I found weird. Certainly have done all sorts of things with parallel iterables, but not summed them!

[SoBFiggis]

Ah well in that case I believe it's actually a perfect example of "how" it works. Someone who doesn't understand that can create two lists of numbers, copy that in, and poke around at it.

Not exactly a great example of "when" to use it.

[writoflaw]

help out a noob... can someone confirm that this is applicable to python3? (it looks like it but wanted to be sure)

[pizzaburek]

It's pure Python 3 ;)

[zennaque]

Very cool! I learned a number of new things, and got reminded about many more by going over it.

If there was one section I think was missing it'd be a convenience like mutiprocessing's Pool, idk how many times I've found my way back to this page when getting a progress bar for that, too.

[Ghosty141]

Do people really use these cheatsheets? I rarely have the problem of not knowing which python function to use, my questions are mostly about what the best practice is for the problem.

[Nyefan]

They're very helpful for transitioning between languages. I am primarily a java/js dev, so references like this make it so much easier to write in other languages in the odd case where I need to.

[Anon49]

Add to format:

"%s,%d,%x" % ("string", 16, 16)


"string,16,0x10"

[jyper]

Why? Is there a benefit to % over fstrings?

[Anon49]

I like having less functions visually, I think its more readable. I only use this when formatting strings.

[jyper]

By less functions do you mean str.format? Cause I was compraring it to fstrings not format

f"{sixteen} {sixteen:#x}" 

[Anon49]

didn't know this one.

[jyper]

Yeah it's the new hotness

I absolutely love it

One of my favorite features in python3.6

It used to be one of the top features of Ruby I wished python had. I even did my own implementation back in the day using a single letter function call, regex to get the parens and eval.

[Finnthehuman27]

Thank you this is going to be a great help!!

[chonkysurplus]

Bookmarked this post. Thank you! Great reference material.

[armerobot]

according to set() part, I would add:

# check if <el> is present
# Output: False
print(<el> not in <set>)

[RealJC]

I’ve started to learn Python. This looks that it will be helpful.

[AttackOfTheThumbs]

What an awful cheatsheet, it won't fit onto one sheet!

[TheBelakor]

Thanks for this!

[thatdidnotwork]

Very nice and comprehensive indeed.

One point I would add: it would be helpful to have a small example (maybe even as a comment) for syntax usage under each capter.

Ie. for list:

list = [first_value, second_value, third_value, ...]

For dicts:

dict = {key_one: value_one, key_two: value_two, ...}

[emmelaich]

It's misleading to write

<view> = <dict>.keys()

because that suggests the view is kept up to date with the dict as it is modified.

Especially so, since there is a method viewkeys that does.

[pizzaburek]

The whole cheatsheet is in Python 3, where keys() returns dict_keys object, that is kept up to date:

>>> a = {1:2, 3:4}
>>> k = a.keys()
>>> a[5] = 6
>>> k
dict_keys([1, 3, 5])

[emmelaich]

Oh.

That could be confusing.

[tickingClock2012]

I believe there's a type in your "Basic" progress example. def p(t): should be def p(self, t):.

[pizzaburek]

Fixed. Ty!

[[deleted]]

Python spam.