6 ms·

Possibly the most interesting anti-pattern I saw was: a_list_of_words = "my list of words".split(" ") I never enquired why, since there were bigger issues in

by scott_w 12y ago

Possibly the most interesting anti-pattern I saw was: a_list_of_words = "my list of words".split(" ") I never enquired why, since there were bigger issues in the code e.g. "unit testing" by running the code, taking the result and putting it as the check value. By running repr(value), copying out the string then comparing self.assertEqual(repr(value), '[<Object1: unicode_value>, ...]')

oddthink 12y ago
I do that all the time in the interpreter, especially when slicing pandas DataFrame objects, e.g.: df_subset = df['date buyer nwidgets'.split()] That is far easier to type than the explicit list, with all its punctuation. Now, it's definitely weird that they did a `split(" ")` rather than just using the default, but the idea is the same. I do try to strip stuff like that out before I put it into a script, replacing it with the explicit list, but I'm never sure if that actually improves anything. It's not as if the explicit list is any easier to read.
- klibertp 12y ago
  It's not weird, it's wrong: In [1]: "a string r".split(" ") Out[1]: ['a', '', '', '', 'string', '', '', '', '', 'r'] In [2]: "a string r".split() Out[2]: ['a', 'string', 'r']
  - glomph 12y ago
    In their case though that wouldn't have been a problem as each word was split on a single space.
  - hcarvalhoalves 12y ago
    Split without argument is equivalent to: >>> filter(None, " quick hack for split".split(" ")) ['quick', 'hack', 'for', 'split']
    - klibertp 12y ago
      Yeah, or re.split(r'\s+', ...), or something - the issue here is that you need to know about this. From the comment a few levels up I understood that the code which used the str.split with " " argument didn't signify that someone who written it knew about its semantics. If he did and it was really what was intended then ofc it's completely ok, but if not, it can easily lead to bugs. For example, if the user is required to input several ints separated with whitespace, this: map(int, input_str.split()) will rise only in expected cases, while this: map(int, input_str.split(" ")) can lead to rejecting correct input just because someone pressed space twice. It's very frustrating for the user, too, because whitespace are hard to spot visually. So, I don't know if this qualifies as antipattern, but I think if I saw .split(" ") instead of .split() in the code I'd at the very least expect the comment explaining why it's used.
- blossoms 12y ago
  I don't mean to be pedantic, but a list (I am assuming df is a list) requires an int. (That sentence I wrote about using hashable types need not apply, sorry!) If you ran that code, you would get this error: TypeError: list indices must be integers, not list
  - gipp 12y ago
    That's a pandas dataframe (idiomatically denoted df), not a list. It has funky slicing properties, and he's selecting columns of the dataframe in a perfectly valid way.
coldtea 12y ago
How is this a real "anti-pattern"? Inefficent, or bizarre way to do it maybe. Anti-pattern is supposed to mean something more, though. In this case there are no adverse effects and no ambiguity -- so, I guess the programmer was just lazy to construct the list.
bkeroack 12y ago
Why even use a list here? Tuples are for immutable/constant data. a_tuple_of_words = ("my", "tuple", "of", "words") or a_tuple_of_words = "my", "tuple", "of", "words"
- dozzie 12y ago
  ...because it's a list? Tuples were supposed to have a structure (at least that's what all the rest of the world thinks of them), so iterating through combination of apples, cars and languages makes no sense whatsoever. But yes, Python misses entirely the point of tuples, treating them as read-only lists. http://dozzie.jogger.pl/2014/04/11/python-tuples-the-useless-thing-in-language/ http://dozzie.jogger.pl/2014/04/11/python-tuples-the-useless...
  - bkeroack 12y ago
    I'm not sure what you're getting at here, or what you are expecting tuples to be like. They can have as much "structure" as you need--they're just a collection. Lighter-weight, immutable collections have a use case. The code in OP appears to be one where it makes sense. I follow the rule where variables are mutable IFF they need to be mutable.
    - dozzie 12y ago
      Tuples by pythonists are used as they were mere lists, just immutable. This is clearly displayed by Python's own interface. For the rest of the world, tuples are not immutable lists. They are tuples, i.e. collections of "objects" that could share nothing about their type. Tuples often are not even iterable! (Erlang, Haskell) The fact that tuples in Python can have as much structure as one wants is derived from dynamic typing, not from the tuples' nature. The same you could say about Python's lists. This is a really subtle issue. It takes to know more languages to see it clearly.
      - bkeroack 12y ago
        If it's so subtle, does it matter? This sounds like you just have a problem with the word "tuple" applied to an object that behaves differently from tuples in a statically-typed language. Would you feel better if they named it "ImmutableList" instead?
james2vegas 12y ago
perhaps that line was written by someone used to Perl, where they would have had @a_list_of_words = qw/my list of words/; there
- dozzie 12y ago
  Or rubyst: a_list_of_words = %w{my list of words}
- rbonvall 12y ago
  You'd be sure if they wrote: >>> qw = str.split >>> qw('my list of words') ['my', 'list', 'of', 'words']
bluecalm 12y ago
This is actually useful: you may want to experiment with different list_of_words in the future and typing the words between [" ", " ", " "] is time consuming. It's also less readable.

by scott_w 12y ago

oddthink 12y ago

I do that all the time in the interpreter, especially when slicing pandas DataFrame objects, e.g.: df_subset = df['date buyer nwidgets'.split()] That is far easier to type than the explicit list, with all its punctuation. Now, it's definitely weird that they did a `split(" ")` rather than just using the default, but the idea is the same. I do try to strip stuff like that out before I put it into a script, replacing it with the explicit list, but I'm never sure if that actually improves anything. It's not as if the explicit list is any easier to read.

klibertp 12y ago
It's not weird, it's wrong: In [1]: "a string r".split(" ") Out[1]: ['a', '', '', '', 'string', '', '', '', '', 'r'] In [2]: "a string r".split() Out[2]: ['a', 'string', 'r']
- glomph 12y ago
  In their case though that wouldn't have been a problem as each word was split on a single space.
- hcarvalhoalves 12y ago
  Split without argument is equivalent to: >>> filter(None, " quick hack for split".split(" ")) ['quick', 'hack', 'for', 'split']
  - klibertp 12y ago
    Yeah, or re.split(r'\s+', ...), or something - the issue here is that you need to know about this. From the comment a few levels up I understood that the code which used the str.split with " " argument didn't signify that someone who written it knew about its semantics. If he did and it was really what was intended then ofc it's completely ok, but if not, it can easily lead to bugs. For example, if the user is required to input several ints separated with whitespace, this: map(int, input_str.split()) will rise only in expected cases, while this: map(int, input_str.split(" ")) can lead to rejecting correct input just because someone pressed space twice. It's very frustrating for the user, too, because whitespace are hard to spot visually. So, I don't know if this qualifies as antipattern, but I think if I saw .split(" ") instead of .split() in the code I'd at the very least expect the comment explaining why it's used.
blossoms 12y ago
I don't mean to be pedantic, but a list (I am assuming df is a list) requires an int. (That sentence I wrote about using hashable types need not apply, sorry!) If you ran that code, you would get this error: TypeError: list indices must be integers, not list
- gipp 12y ago
  That's a pandas dataframe (idiomatically denoted df), not a list. It has funky slicing properties, and he's selecting columns of the dataframe in a perfectly valid way.

coldtea 12y ago

How is this a real "anti-pattern"? Inefficent, or bizarre way to do it maybe. Anti-pattern is supposed to mean something more, though. In this case there are no adverse effects and no ambiguity -- so, I guess the programmer was just lazy to construct the list.

bkeroack 12y ago

Why even use a list here? Tuples are for immutable/constant data. a_tuple_of_words = ("my", "tuple", "of", "words") or a_tuple_of_words = "my", "tuple", "of", "words"

dozzie 12y ago
...because it's a list? Tuples were supposed to have a structure (at least that's what all the rest of the world thinks of them), so iterating through combination of apples, cars and languages makes no sense whatsoever. But yes, Python misses entirely the point of tuples, treating them as read-only lists. http://dozzie.jogger.pl/2014/04/11/python-tuples-the-useless-thing-in-language/ http://dozzie.jogger.pl/2014/04/11/python-tuples-the-useless...
- bkeroack 12y ago
  I'm not sure what you're getting at here, or what you are expecting tuples to be like. They can have as much "structure" as you need--they're just a collection. Lighter-weight, immutable collections have a use case. The code in OP appears to be one where it makes sense. I follow the rule where variables are mutable IFF they need to be mutable.
  - dozzie 12y ago
    Tuples by pythonists are used as they were mere lists, just immutable. This is clearly displayed by Python's own interface. For the rest of the world, tuples are not immutable lists. They are tuples, i.e. collections of "objects" that could share nothing about their type. Tuples often are not even iterable! (Erlang, Haskell) The fact that tuples in Python can have as much structure as one wants is derived from dynamic typing, not from the tuples' nature. The same you could say about Python's lists. This is a really subtle issue. It takes to know more languages to see it clearly.
    - bkeroack 12y ago
      If it's so subtle, does it matter? This sounds like you just have a problem with the word "tuple" applied to an object that behaves differently from tuples in a statically-typed language. Would you feel better if they named it "ImmutableList" instead?

james2vegas 12y ago

perhaps that line was written by someone used to Perl, where they would have had @a_list_of_words = qw/my list of words/; there

dozzie 12y ago
Or rubyst: a_list_of_words = %w{my list of words}
rbonvall 12y ago
You'd be sure if they wrote: >>> qw = str.split >>> qw('my list of words') ['my', 'list', 'of', 'words']

bluecalm 12y ago

This is actually useful: you may want to experiment with different list_of_words in the future and typing the words between [" ", " ", " "] is time consuming. It's also less readable.