Take for example: [str(x) for i in range(3) for x in foo(i)]
Let's decompose it:
def foo(i):
return i, i + 0.5
[str(x)
for i in range(3)
for x in foo(i)
]
# is same as
for i in range(3):
for x in foo(i):
yield str(x)
@continue There are two differences:
1) The second version is not legal out of context; you can only use yield inside a function definition.
2) Even if the second is corrected to
def g():
for i in range(3):
for x in foo(i):
yield str(x)
g()
then you get a generator, not a list. It would be equivalent to the first version if you changed the last line to:
list(g())
A more direct translation might be:
result = []
for i in range(3):
for x in foo(i):
result.append(str(x))
result
Your larger point, that the order of the for loops is the same whether you use lists comprehensions or actual nested loops, still holds.
Personally, I avoid this sort of nested comprehension because of just this sort of confusion. It's also counterintuitive because you can't "unpack" it in the usual way by adding brackets.
[str(x) for i in range(3) for x in foo(i)]
does not produce the same result as:
[[str(x) for i in range(3)] for x in foo(i)]
This is interesting, thanks.
I was initially confused by the order of iteration over two for.