[issue18474] Lambda assigned to object does not automatically get self

[James Lu]

New submission from James Lu:

if you assign a lambda to a object and call it,you get this:
Traceback (most recent call last):
  File pyshell#21, line 1, in module
n.__div__(3)
TypeError: lambda() takes exactly 2 arguments (1 given)
The full test is here:
 n = num()
 n.__div__
function lambda at 0x040B2DF0
 n/3
Traceback (most recent call last):
  File pyshell#20, line 1, in module
n/3
TypeError: unsupported operand type(s) for /: 'num' and 'int'
 n.__div__(3)
Traceback (most recent call last):
  File pyshell#21, line 1, in module
n.__div__(3)
TypeError: lambda() takes exactly 2 arguments (1 given)

--
messages: 193166
nosy: James.Lu
priority: normal
severity: normal
status: open
title: Lambda assigned to object does not automatically get self

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[issue18474] Lambda assigned to object does not automatically get self

[James Lu]

Changes by James Lu jam...@gmail.com:


--
type:  - behavior

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[issue18474] Lambda assigned to object does not automatically get self

[Brett Cannon]

Brett Cannon added the comment:

What version of Python is this and did you assign the lambda to an instance or 
class (and if this is Python 2, new-style or classic class)?

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nosy: +brett.cannon

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[issue18474] Lambda assigned to object does not automatically get self

[James Lu]

James Lu added the comment:

2.5,new-style

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[issue18474] Lambda assigned to object does not automatically get self

[James Lu]

James Lu added the comment:

instance,assinged during __init__

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[issue18474] Lambda assigned to object does not automatically get self

[James Lu]

James Lu added the comment:

Also,there were some bugs, but after I fixed them, it would only work if I did 
this:
n.__div__(n,3)

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[issue18474] Lambda assigned to object does not automatically get self

[Eric V. Smith]

Eric V. Smith added the comment:

Could you provide an entire example, showing the class num and how you assign 
__div__?

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nosy: +eric.smith

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[issue18474] Lambda assigned to object does not automatically get self

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc added the comment:

This is expected. When you assign to n.__div__ a function which takes two 
parameters, you have to call it with two parameters:

aFunction = lambda x, y: (x, y)
n.__div__ = aFunction
aFunction(1, 2)
n.__div__(1, 2)

After all, aFunction and n.__div__ are the same object.
Now, it would be different if you had attached the function to the *class* 
instead:

n.__class__.__div__ = aFunction
n.__div__(2)   # returns (n, 2)

In this second example, n.__div__ is a bound method; the first parameter 
(usually named self) is already filled, and only the second one is required.

--
nosy: +amaury.forgeotdarc
resolution:  - invalid
status: open - closed

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