4 ms·

Neat little story, despite the grammar and capitalization. Is it common to use _ as an index variable? Edit: for _ in range(4):

JosephHatfield 14y ago
Not sure how common that is, but I've seen it used before where the index variable itself is not referenced inside the body of the statement.
mikeash 14y ago
_ is a typical name to use when the language requires a variable name that the program doesn't otherwise need. In this case, the program just needs to run some code four times, and doesn't care about the index. The language doesn't have a plain "run this code X times" construct, but it does have a "iterate over this list" construct, so the code iterates over the list [0, 1, 2, 3] and puts the current element into a dummy variable since it's not being used.
- deleted 14y ago
  [deleted]
monochromatic 14y ago
I've seen it before, but it's a little jarring. Not sure what's wrong with just using i.
- jdiez17 14y ago
  It says explicitly that you don't care about that value. If you used i, for example, you wouldn't know whether the loop depended on the iteration number.
  - monochromatic 14y ago
    Yeah, I get it. And that's a useful thing to do, I guess. It just seems a little... unpythonic.
- randomsearch 14y ago
  To avoid unused variable warnings.
aghull 14y ago
Common in Lua, Ruby, Python. In fact, ruby gives _ a minor amount of special meaning to make it more convenient as a throw-away variable, e.g. it can be specified multiple times in an argument list without an error and generates no warning if left unused.
yen223 14y ago
It's better to use two underscores __ to represent throwaway variables, because _ has a meaning in Python: it returns the last output.
- GuiA 14y ago
  True, but only in the REPL. For example try to run the following script (not from the REPL): _ = 12 print _ 42 * 42 print _
mertd 14y ago
Most of the code is a little verbose for Python. For example make() function could simply be: return [random.randint(1,10000) for x in range(4)] Also remember that a little kitten dies every time you write a for loop as follows: for index in range(len(some_list)):
- ipince 14y ago
  I'm a python noob. Why does a kitten die? You're creating a new list of the same size of the source list (once) and iterating over it. How can you achieve the same w/out creating a new list?
  - mertd 14y ago
    Python god takes the kitten as a sacrifice for the unnecessary list of indexes you created :). range(len(some_list)) is a convoluted way iterating over the elements of a list. What you are doing is creating a new list with elements [0,... lengh-1] and iterating over the elements of this list, only to immediately throw them away after using them as array index to grab the item you really want from the original list. Instead you can just directly iterate over your original list: "for item in some_list". If you really need to know the index value, you can use enumerate: "for index, item in enumerate(some_list)" One nice thing is that the "for x in y" lets you iterate over things (iterables) that you may be generating on the fly (e.g., all prime numbers smaller than N).

JosephHatfield 14y ago

Not sure how common that is, but I've seen it used before where the index variable itself is not referenced inside the body of the statement.

mikeash 14y ago

_ is a typical name to use when the language requires a variable name that the program doesn't otherwise need. In this case, the program just needs to run some code four times, and doesn't care about the index. The language doesn't have a plain "run this code X times" construct, but it does have a "iterate over this list" construct, so the code iterates over the list [0, 1, 2, 3] and puts the current element into a dummy variable since it's not being used.

deleted 14y ago
[deleted]

monochromatic 14y ago

I've seen it before, but it's a little jarring. Not sure what's wrong with just using i.

jdiez17 14y ago
It says explicitly that you don't care about that value. If you used i, for example, you wouldn't know whether the loop depended on the iteration number.
- monochromatic 14y ago
  Yeah, I get it. And that's a useful thing to do, I guess. It just seems a little... unpythonic.
randomsearch 14y ago
To avoid unused variable warnings.

aghull 14y ago

Common in Lua, Ruby, Python. In fact, ruby gives _ a minor amount of special meaning to make it more convenient as a throw-away variable, e.g. it can be specified multiple times in an argument list without an error and generates no warning if left unused.

yen223 14y ago

It's better to use two underscores __ to represent throwaway variables, because _ has a meaning in Python: it returns the last output.

GuiA 14y ago
True, but only in the REPL. For example try to run the following script (not from the REPL): _ = 12 print _ 42 * 42 print _

mertd 14y ago

Most of the code is a little verbose for Python. For example make() function could simply be: return [random.randint(1,10000) for x in range(4)] Also remember that a little kitten dies every time you write a for loop as follows: for index in range(len(some_list)):

ipince 14y ago
I'm a python noob. Why does a kitten die? You're creating a new list of the same size of the source list (once) and iterating over it. How can you achieve the same w/out creating a new list?
- mertd 14y ago
  Python god takes the kitten as a sacrifice for the unnecessary list of indexes you created :). range(len(some_list)) is a convoluted way iterating over the elements of a list. What you are doing is creating a new list with elements [0,... lengh-1] and iterating over the elements of this list, only to immediately throw them away after using them as array index to grab the item you really want from the original list. Instead you can just directly iterate over your original list: "for item in some_list". If you really need to know the index value, you can use enumerate: "for index, item in enumerate(some_list)" One nice thing is that the "for x in y" lets you iterate over things (iterables) that you may be generating on the fly (e.g., all prime numbers smaller than N).