On 31/05/2021 17:57, Colin McPhail via Python-list wrote:
Hi,
According to the enum module's documentation an Enum-based enumeration's
members can have values of any type:
"Member values can be anything: int, str, etc.."
You didn't read the fineprint ;)
"""
The rules for what is allowed are as follows: names that start and end
with a single underscore are reserved by enum and cannot be used; all
other attributes defined within an enumeration will become members of
this enumeration, with the exception of special methods (__str__(),
__add__(), etc.), descriptors (methods are also descriptors), and
variable names listed in _ignore_
""""
Functions written in Python are descriptors and therefore cannot be
used. Builtin functions aren't, leading to the following somewhat
surprising difference:
>>> def foo(self): print("foo")
>>> class A(Enum):
x = foo # foo.__get__ exists -> foo is a descriptor
# the enum library assumes you are adding a
# method to your
# class, not an enumeration value.
y = sum # no sum.__get__ attribute -> function
# treated as an enumeration value.
>>> list(A)
[<A.y: <built-in function sum>>]
>>> A.x
<function foo at 0x012096A0>
>>> A.y
<A.y: <built-in function sum>>
>>> A.y.x()
foo
I defined one with functions as member values. This seemed to work as long as the functions
were defined ahead of the enumeration's definition. However I then noticed that my
enumeration class was a bit weird: even although I could reference the enumeration's
members individually by name I couldn't iterate through the members in the normal fashion -
it seemed to have no members. Also, calling type() on a member gave the result <class
'function'> instead of the expected <enum 'enum name'>.
I am using Python 3.9.5 from python.org on macOS 11.4. Below is a small test
script and its output. Are my expectations wrong or is there a problem with
Enum?
Regards,
Colin
-------------------------------
from enum import Enum
def connect_impl():
print("message from connect_impl()")
def help_impl():
print("message from help_impl()")
class Command1(Enum):
CONNECT = 1
HELP = 2
class Command2(Enum):
CONNECT = connect_impl
HELP = help_impl
if __name__ == "__main__":
def print_enum(cls, mbr):
print(f"{cls.__name__}\n type(): {type(Command1)}")
print(f" type of enum member: {type(mbr)}")
print(f" number of members: {len(cls)}")
print(" enum members:")
if len(cls) > 0:
for c in cls:
print(f" {c}")
else:
print(" <none>")
print(f" dir(): {dir(cls)}")
member_1 = Command1.HELP
print_enum(Command1, member_1)
print()
member_2 = Command2.HELP
print_enum(Command2, member_2)
print()
print("call Command2 member: ", end="")
member_2()
print()
-------------------------------
(qt6) % python3 try_enum.py
Command1
type(): <class 'enum.EnumMeta'>
type of enum member: <enum 'Command1'>
number of members: 2
enum members:
Command1.CONNECT
Command1.HELP
dir(): ['CONNECT', 'HELP', '__class__', '__doc__', '__members__',
'__module__']
Command2
type(): <class 'enum.EnumMeta'>
type of enum member: <class 'function'>
number of members: 0
enum members:
<none>
dir(): ['__class__', '__doc__', '__members__', '__module__']
call Command2 member: message from help_impl()
(qt6) %
-------------------------------
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