learning python ...

[hw]

On 5/23/21 7:28 PM, Peter Otten wrote:
> On 23/05/2021 06:37, hw wrote:
>>
>> Hi,
>>
>> I'm starting to learn python and have made a little example program 
>> following a tutorial[1] I'm attaching.
>>
>> Running it, I'm getting:
>>
>>
>> Traceback (most recent call last):
>>    File "[...]/hworld.py", line 18, in <module>
>>      print(isinstance(int, float))
>> TypeError: isinstance() arg 2 must be a type or tuple of types
>>
>>
>> I would understand to get an error message in line 5 but not in 18.  
>> Is this a bug or a feature?
> 
> It is a bug in your code (which you don't provide). Did you assign some 
> value to float, e. g.:
> 
>  >>> float = 42.0
>  >>> isinstance(int, float)
> Traceback (most recent call last):
>    File "<pyshell#313>", line 1, in <module>
>      isinstance(int, float)
> TypeError: isinstance() arg 2 must be a type or tuple of types
> 
> If you do not shadow the built-in you should get
> 
>  >>> isinstance(int, float)
> False
> 

Apparently the attachment was stripped from my message.  I'll put a 
smaller version directly into this message instead of an attachment:


#!/usr/bin/python

print("world!")

int = 17
print("world", int)

float = 6.670
print("world", float)

foo = 0
print(type(int))
print(type(float))
print(type(foo))

print(isinstance(foo, str))
print(isinstance(int, float))
print(isinstance(float, float))


I don't know about shadowing.  If I have defeated a whole variable type 
by naming a variable like a variable type, I would think it is a bad 
idea for python to allow this without warning.  It seems like a recipie 
for creating chaos.