Given a #Python list of numeric strings:
x = ['1', '2', '3']
I can try to use "sum(mylist)". But that'll fail, because they're strings. I can use a list comprehension to convert them:
sum([int(y)
for y in x])
But it also works without the []:
sum(int(y)
for y in x)
Huh?
x = ['1', '2', '3']
I can try to use "sum(mylist)". But that'll fail, because they're strings. I can use a list comprehension to convert them:
sum([int(y)
for y in x])
But it also works without the []:
sum(int(y)
for y in x)
Huh?
List comprehensions return (by definition) lists. So this:
[int(y)
for y in x]
returns a list -- in this case, a list of ints. The list is returned all at once, though.
[int(y)
for y in x]
returns a list -- in this case, a list of ints. The list is returned all at once, though.
To save memory, it's often best to use a generator comprehension:
(int(y)
for y in x)
This doesn't return a list. Rather, it returns a generator, an object that knows how to behave in a "for" loop. You can say:
g = (int(y) for y in x)
for i in g:
print(i) # 1, 2, 3
(int(y)
for y in x)
This doesn't return a list. Rather, it returns a generator, an object that knows how to behave in a "for" loop. You can say:
g = (int(y) for y in x)
for i in g:
print(i) # 1, 2, 3
I can use a generator where an iterable is wanted. For example, the builtin "sum" function:
sum((int(y)
for y in x))
Notice the double parentheses? Turns out you don't need them!
sum(int(y)
for y in x)
Python sees the generator expression, and does the right thing.
sum((int(y)
for y in x))
Notice the double parentheses? Turns out you don't need them!
sum(int(y)
for y in x)
Python sees the generator expression, and does the right thing.
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