8 ms·

Python Cheat Sheet for Work

24 points by kusanagiblade 11y ago

japhyr 11y ago
If anyone is new to Python and looking for a more complete set of cheat sheets, I recently developed a set aimed at beginners. Rather than simply list syntax, there's a brief summary of many core concepts in Python. I thought this might be more helpful to true beginners than a set of sheets that focus purely on syntax. Overview of cheat sheets, and links to individual cheat sheets: - http://ehmatthes.github.io/pcc/cheatsheets/README.html http://ehmatthes.github.io/pcc/cheatsheets/README.html All cheat sheets in the set, in one pdf: - https://github.com/ehmatthes/pcc/raw/master/cheat_sheets/beginners_python_cheat_sheet_pcc_all.pdf https://github.com/ehmatthes/pcc/raw/master/cheat_sheets/beg...
- flashm 11y ago
  These are excellent. I don't use Python that often so something like this is perfect to refresh each time and to avoid doing anything unidiomatic. 'Learn X in Y' is also a useful site for this sort of thing.
sago 11y ago
I was a bit bemused by this, sorry. eg. `(a += b) == a + b` is not true, a += b is not an expression. `str.is_digit()` doesn't 'check number', it checks if the string is entirely composed of unicode digit codepoints. `dict(col)` doesn't work for a general collection `dict([1,2,3])` for example. Are these really the things people forget the most coming from another language? Not try/raise/except/finally? Negative indices? If it works, it works, good on you for making it (and making it look good), but in general, it seems to be a bit insubstantial.
- nvader 11y ago
  I think this was an April Fool's Gag, although I'm not 100% clear on this. It certainly should be, if not :P
- aidos 11y ago
  I don't think that expression was meant to evaluate to True - they were just reminding themselves that you can increment by an amount using += in Python. This list of full of basic stuff though, and people who were referring to this would write insainly non-idiomatic Python, but hey, you gotta start somewhere. When I went to doing Python full time (after having built stuff in it on and off for years) it took me a good 6 months before I was able to write idiomatic Python. That's with over 15 years development experience and actively reading lots of nice Python code to try to reach the same level. Reading something like this reminds me of the gulf between, "can code in Python" and "writes nice code in Python".
- amelius 11y ago
  > (a += b) == a + b Solution: b == 0
  - kusanagiblade 11y ago
    I do have to apologize for that piece of code... I wrote it down more of a reminder... I didn't check the syntax if it works. I guess not. It will be fixed.
- id 11y ago
  I don't even know why this is on the front page. It's incomplete, inaccurate and just very low quality. And it's strange that they would use this font for code.
- noobie 11y ago
  >`str.is_digit()` doesn't 'check number', it checks if the string is entirely composed of unicode digit codepoints. What do you mean?
  - epidemian 11y ago
    I'm not really sure. Maybe that: >>> u'0١߂३৪੫૬୭௮౯'.isdigit() True So it's not equivalent to matching [0-9]+, which some people might expect. It's quite nice i think, because apparently int() supports Unicode numeric characters too (i didn't know this): >>> int(u'0١߂३৪੫૬୭௮౯') 123456789
    - sago 11y ago
      Right - `isdigit` checks for membership in unicode class Nd. So the other decimal digits you quote work. Similarly `int()` supports the same values. `isdigit` doesn't support Nl or No class digits (not even ones corresponding to decimal digits, like Ⅳ). I don't know if it is possible to construct an example where `isdigit` would return True but `int` would fail. It wouldn't surprise me, either way, but at the least the failure case isn't obvious. The real problem is the converse `"1.23".isdigit()` returns False, where 1.23 is a number, so it doesn't 'check number'. And `int("-23")` works, but `"-23".isdigit()` is False. You could argue it 'checks non-negative integer'. I happened upon a stack exchange answer a while back, accepted, that failed because of this bug. In general the Python way to check if one thing can be converted into another is to try, and trap the error. def isnumber(text): try: float(text) except ValueError: return False else: return True
- kusanagiblade 11y ago
  I like the try/raise/except. Good one. Will add it in there.
ADSSDA 11y ago
I'm hoping this is some sort of late april fools post? This cheat sheet is stuff no python programmer would need to look up, and even then, manages to get a few things wrong.
nvader 11y ago
I feel like the author is missing something fundamental about the appropriateness of "cheat sheets" to certain domains of knowledge. The poll on that page shows an overwhelming majority (>75%) of people are ambivalent or skeptical of a Python cheat sheet.
jake-low 11y ago
Imagine you're interviewing someone for an intro-level full stack position, where they'd be writing JavaScript and Python. You ask them a whiteboard coding question -- something about manipulating strings or implementing simple searching. Let's ignore the debate of whether this is a productive technique for interviews for now. You ask for Python in this question since you've already covered JavaScript. The candidate can't remember what the "str" type is called, or how to find substrings in a string, or the difference between "==" and "is" for objects. They ask you to remind them if "join" is a method on sequences or on strings. They write "length()" when they mean "len()". We've discussed at length on HN the challenges of whiteboard coding. "Nobody's favorite IDE is their conference room whiteboard". But I feel that, even through the flawed medium of the whiteboard, I'm seeing symptoms of the candidate not really "knowing" Python to the degree I would expect of someone who applied for a job writing it. None of the people I work with who write Python would ever forget one of these basics. I think they recognize that the ultimate "efficiency" isn't a cheat sheet on your wall, but rather learning and internalizing these tools by repeatedly using them. Forgive me for setting up what I recognize to be a straw-man argument. Not everyone who writes Python was hired for their ability to do it. Maybe the candidate is a stellar JavaScript developer, and their only Python weaknesses are with the syntax and standard library. Perhaps a cheat sheet is an effective way to bridge the gap between "learning" and "internalizing" a language's features. Nonetheless, I'd like to hear people's thoughts on the hypothetical situation above (or another better one, if you feel the one I've chosen is biased or misses the point).
- deleted 11y ago
  [deleted]
- WoodenChair 11y ago
  I definitely get what you're saying, but it really depends on whether you're hiring someone to be a Python expert, or someone to be a great software developer. If you need a Python expert (someone who knows the ins and outs of the language right off the bat), you're absolutely right. If you need more generally just a great software developer though, as long as they can show they're a great programmer in a couple different languages and paradigms, whether or not they remember the specifics of how to do String operations in Python, is irrelevant. They can learn that pretty easily. It also depends on whether or not the job in question asked for tons of Python experience as a requirement, or if software development experience was required but only familiarity with Python specifically.
noobie 11y ago
I am not even at an intermediate level of Python and I knew all of the content, either I am better than I thought I am or this cheat sheet is a joke. I'd say it's the latter.
alialkhatib 11y ago
While the author of the post makes it clear that this is for developers, I think this kind of cheat sheet has some value for non-developers. Stuff like recognizing how to run a python script, how to enter the python shell, etc... all sounds like really trivial stuff that we should all know, but if I gave a crash course in Python to someone who primarily used Excel to do data analysis and parsing and whatnot, then this cheat sheet would be useful (I think). It's the little reminders that act as bridges between the gap of learning and internalizing something, as jake-low mentions. I probably wouldn't give them this PDF, but I imagine I would give them a markdown file that illustrates many of these same reminders with examples and caveats. It's confusing that the author specifically says that the startup works with Python and Django, because I agree that a Python developer shouldn't need a reminder that `python <file.py>` runs the python script (and in fact in that space I would have instead made a note about `python`/`python3`) but I want to try to take the value from this, rather than pile on with the crowd deriding it.

24 points by kusanagiblade 11y ago

If anyone is new to Python and looking for a more complete set of cheat sheets, I recently developed a set aimed at beginners. Rather than simply list syntax, there's a brief summary of many core concepts in Python. I thought this might be more helpful to true beginners than a set of sheets that focus purely on syntax. Overview of cheat sheets, and links to individual cheat sheets: - http://ehmatthes.github.io/pcc/cheatsheets/README.html http://ehmatthes.github.io/pcc/cheatsheets/README.html All cheat sheets in the set, in one pdf: - https://github.com/ehmatthes/pcc/raw/master/cheat_sheets/beginners_python_cheat_sheet_pcc_all.pdf https://github.com/ehmatthes/pcc/raw/master/cheat_sheets/beg...

flashm 11y ago
These are excellent. I don't use Python that often so something like this is perfect to refresh each time and to avoid doing anything unidiomatic. 'Learn X in Y' is also a useful site for this sort of thing.

sago 11y ago

I was a bit bemused by this, sorry. eg. `(a += b) == a + b` is not true, a += b is not an expression. `str.is_digit()` doesn't 'check number', it checks if the string is entirely composed of unicode digit codepoints. `dict(col)` doesn't work for a general collection `dict([1,2,3])` for example. Are these really the things people forget the most coming from another language? Not try/raise/except/finally? Negative indices? If it works, it works, good on you for making it (and making it look good), but in general, it seems to be a bit insubstantial.

nvader 11y ago
I think this was an April Fool's Gag, although I'm not 100% clear on this. It certainly should be, if not :P
aidos 11y ago
I don't think that expression was meant to evaluate to True - they were just reminding themselves that you can increment by an amount using += in Python. This list of full of basic stuff though, and people who were referring to this would write insainly non-idiomatic Python, but hey, you gotta start somewhere. When I went to doing Python full time (after having built stuff in it on and off for years) it took me a good 6 months before I was able to write idiomatic Python. That's with over 15 years development experience and actively reading lots of nice Python code to try to reach the same level. Reading something like this reminds me of the gulf between, "can code in Python" and "writes nice code in Python".
amelius 11y ago
> (a += b) == a + b Solution: b == 0
- kusanagiblade 11y ago
  I do have to apologize for that piece of code... I wrote it down more of a reminder... I didn't check the syntax if it works. I guess not. It will be fixed.
id 11y ago
I don't even know why this is on the front page. It's incomplete, inaccurate and just very low quality. And it's strange that they would use this font for code.
noobie 11y ago
>`str.is_digit()` doesn't 'check number', it checks if the string is entirely composed of unicode digit codepoints. What do you mean?
- epidemian 11y ago
  I'm not really sure. Maybe that: >>> u'0١߂३৪੫૬୭௮౯'.isdigit() True So it's not equivalent to matching [0-9]+, which some people might expect. It's quite nice i think, because apparently int() supports Unicode numeric characters too (i didn't know this): >>> int(u'0١߂३৪੫૬୭௮౯') 123456789
  - sago 11y ago
    Right - `isdigit` checks for membership in unicode class Nd. So the other decimal digits you quote work. Similarly `int()` supports the same values. `isdigit` doesn't support Nl or No class digits (not even ones corresponding to decimal digits, like Ⅳ). I don't know if it is possible to construct an example where `isdigit` would return True but `int` would fail. It wouldn't surprise me, either way, but at the least the failure case isn't obvious. The real problem is the converse `"1.23".isdigit()` returns False, where 1.23 is a number, so it doesn't 'check number'. And `int("-23")` works, but `"-23".isdigit()` is False. You could argue it 'checks non-negative integer'. I happened upon a stack exchange answer a while back, accepted, that failed because of this bug. In general the Python way to check if one thing can be converted into another is to try, and trap the error. def isnumber(text): try: float(text) except ValueError: return False else: return True
kusanagiblade 11y ago
I like the try/raise/except. Good one. Will add it in there.

ADSSDA 11y ago

I'm hoping this is some sort of late april fools post? This cheat sheet is stuff no python programmer would need to look up, and even then, manages to get a few things wrong.

nvader 11y ago

I feel like the author is missing something fundamental about the appropriateness of "cheat sheets" to certain domains of knowledge. The poll on that page shows an overwhelming majority (>75%) of people are ambivalent or skeptical of a Python cheat sheet.

jake-low 11y ago

Imagine you're interviewing someone for an intro-level full stack position, where they'd be writing JavaScript and Python. You ask them a whiteboard coding question -- something about manipulating strings or implementing simple searching. Let's ignore the debate of whether this is a productive technique for interviews for now. You ask for Python in this question since you've already covered JavaScript. The candidate can't remember what the "str" type is called, or how to find substrings in a string, or the difference between "==" and "is" for objects. They ask you to remind them if "join" is a method on sequences or on strings. They write "length()" when they mean "len()". We've discussed at length on HN the challenges of whiteboard coding. "Nobody's favorite IDE is their conference room whiteboard". But I feel that, even through the flawed medium of the whiteboard, I'm seeing symptoms of the candidate not really "knowing" Python to the degree I would expect of someone who applied for a job writing it. None of the people I work with who write Python would ever forget one of these basics. I think they recognize that the ultimate "efficiency" isn't a cheat sheet on your wall, but rather learning and internalizing these tools by repeatedly using them. Forgive me for setting up what I recognize to be a straw-man argument. Not everyone who writes Python was hired for their ability to do it. Maybe the candidate is a stellar JavaScript developer, and their only Python weaknesses are with the syntax and standard library. Perhaps a cheat sheet is an effective way to bridge the gap between "learning" and "internalizing" a language's features. Nonetheless, I'd like to hear people's thoughts on the hypothetical situation above (or another better one, if you feel the one I've chosen is biased or misses the point).

deleted 11y ago
[deleted]
WoodenChair 11y ago
I definitely get what you're saying, but it really depends on whether you're hiring someone to be a Python expert, or someone to be a great software developer. If you need a Python expert (someone who knows the ins and outs of the language right off the bat), you're absolutely right. If you need more generally just a great software developer though, as long as they can show they're a great programmer in a couple different languages and paradigms, whether or not they remember the specifics of how to do String operations in Python, is irrelevant. They can learn that pretty easily. It also depends on whether or not the job in question asked for tons of Python experience as a requirement, or if software development experience was required but only familiarity with Python specifically.

noobie 11y ago

I am not even at an intermediate level of Python and I knew all of the content, either I am better than I thought I am or this cheat sheet is a joke. I'd say it's the latter.

alialkhatib 11y ago

While the author of the post makes it clear that this is for developers, I think this kind of cheat sheet has some value for non-developers. Stuff like recognizing how to run a python script, how to enter the python shell, etc... all sounds like really trivial stuff that we should all know, but if I gave a crash course in Python to someone who primarily used Excel to do data analysis and parsing and whatnot, then this cheat sheet would be useful (I think). It's the little reminders that act as bridges between the gap of learning and internalizing something, as jake-low mentions. I probably wouldn't give them this PDF, but I imagine I would give them a markdown file that illustrates many of these same reminders with examples and caveats. It's confusing that the author specifically says that the startup works with Python and Django, because I agree that a Python developer shouldn't need a reminder that `python <file.py>` runs the python script (and in fact in that space I would have instead made a note about `python`/`python3`) but I want to try to take the value from this, rather than pile on with the crowd deriding it.