[Python-ideas] Multi Statement Lambdas

[Serhiy Storchaka]

22.10.18 02:16, Terry Reedy пише:
> All 
> functions created from lambda expressions get the same pseudo-name 
> '<lambda>'.  This can make tracebacks worse.  Perhaps more importantly, 
> proper testing may become harder.

See https://bugs.python.org/issue34856. But this can work only while 
lambda's body is a simple expression.

>  >>> for i in map(lambda x: x **
>            2, 'abc'):
>      print(i)
> 
> Traceback (most recent call last):
>    File "<pyshell#19>", line 2, in <module>
>      2, 'abc'):
>    File "<pyshell#19>", line 2, in <lambda>
>      2, 'abc'):
> TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int'

In 3.8 the traceback is different (an can be even more informative with 
resolved issue34856).

Traceback (most recent call last):
   File "1.py", line 1, in <module>
     for i in map(lambda x: x **
   File "1.py", line 1, in <lambda>
     for i in map(lambda x: x **
TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int'

> Given that there might be a hundred functions named '<lambda>', I think 
> the specific name is a bit helpful.

I think the main problem is not with tracebacks, but with reprs. If you 
have a pack of callbacks, it is not easy to figure out what they do if 
they are anonymous functions.