How do I annotate types in a for-loop?
PythonFor LoopPycharmType HintingPython TypingPython Problem Overview
I want to annotate a type of a variable in a for-loop. I tried this but it didn't work:
for i: int in range(5):
pass
What I expect is working autocomplete in PyCharm 2016.3.2, but using pre-annotation didn't work:
i: int
for i in range(5):
pass
P.S. Pre-annotation works for PyCharm >= 2017.1.
Python Solutions
Solution 1 - Python
According to PEP 526, this is not allowed:
> In addition, one cannot annotate variables used in a for or with
> statement; they can be annotated ahead of time, in a similar manner to
> tuple unpacking
Annotate it before the loop:
i: int
for i in range(5):
pass
PyCharm 2018.1 and up now recognizes the type of the variable inside the loop. This was not supported in older PyCharm versions.
Solution 2 - Python
I don't know if this solution is PEP-compatible or just a feature of PyCharm, but I made it work like this:
for i in range(5): #type: int
pass
and I'm using Pycharm Community Edition 2016.2.1
Solution 3 - Python
This works well for my in PyCharm (using Python 3.6)
for i in range(5):
i: int = i
pass
Solution 4 - Python
None of the responses here were useful, except to say that you can't. Even the accepted answer uses syntax from the PEP 526 document, which isn't valid python syntax. If you try to type in
x: int
You'll see it's a syntax error.
Here is a useful workaround:
for __x in range(5):
x = __x # type: int
print(x)
Do your work with x. PyCharm recognizes its type, and autocomplete works.