Type hint for a file or file-like object?
Question:
Is there any correct type hint to use for a file or file-like object in Python? For example, how would I type-hint the return value of this function?
def foo() -> ???:
return open('bar')
Answers:
Use either the typing.TextIO or typing.BinaryIO types, for files opened in text mode or binary mode respectively.
From the docs:
class typing.IO
Wrapper namespace for I/O stream types.
This defines the generic type IO[AnyStr] and aliases TextIO and BinaryIO for respectively IO[str] and IO[bytes]. These representing the types of I/O streams such as returned by open().
The short answer:
- You need to be explicit. That is
from typing import TextIO not just from typing import *.
- Use
IO to mean a file without specifying what kind
- Use
TextIO or BinaryIO if you know the type
- You cannot currently specify it be opened for write or its encoding.
As an example:
from typing import BinaryIO
def binf(inf: BinaryIO):
pass
with open('x') as f:
binf(f)
gives an inspection error (in PyCharm) of Expected type 'BinaryIO', got 'TextIO' instead
Is there any correct type hint to use for a file or file-like object in Python? For example, how would I type-hint the return value of this function?
def foo() -> ???:
return open('bar')
Use either the typing.TextIO or typing.BinaryIO types, for files opened in text mode or binary mode respectively.
From the docs:
class
typing.IOWrapper namespace for I/O stream types.
This defines the generic type
IO[AnyStr]and aliasesTextIOandBinaryIOfor respectivelyIO[str]andIO[bytes]. These representing the types of I/O streams such as returned byopen().
The short answer:
- You need to be explicit. That is
from typing import TextIOnot justfrom typing import *. - Use
IOto mean a file without specifying what kind - Use
TextIOorBinaryIOif you know the type - You cannot currently specify it be opened for write or its encoding.
As an example:
from typing import BinaryIO
def binf(inf: BinaryIO):
pass
with open('x') as f:
binf(f)
gives an inspection error (in PyCharm) of Expected type 'BinaryIO', got 'TextIO' instead