function object.func_default off the console

[Aaron Brady]

>>f.func_defaults[0]
[2, 3]

>>f.func_defaults[0]+=[4]

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

>>f.func_defaults[0]

[2, 3, 4]

V. interesting. Operation succeeds but with a throw. Er, raise.

[Peter Otten]

Aaron Brady wrote:

>>>f.func_defaults[0]

[2, 3]

>>>f.func_defaults[0]+=[4]

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

>>>f.func_defaults[0]

[2, 3, 4]

V. interesting. Operation succeeds but with a throw. Er, raise.

This is not specific to func_defaults:

>>t = ([1],)
t[0] += [2]

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

>>t

([1, 2],)

t[0] += [2]

is resolved to

t.__setitem__(t[0].__iadd__([2]))

where list.__iadd__() succeeds but __setitem__() fails (because tuples don't
have that method).

Peter

[castironpi]

On Apr 25, 1:56 am, Peter Otten <[e-mail]:

Aaron Brady wrote:

>>f.func_defaults[0]

[2, 3]

>>f.func_defaults[0]+=[4]

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

>>f.func_defaults[0]

[2, 3, 4]

V. interesting. Operation succeeds but with a throw. Er, raise.

This is not specific to func_defaults:

>t = ([1],)
t[0] += [2]

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment>>t

([1, 2],)

t[0] += [2]

is resolved to

t.__setitem__(t[0].__iadd__([2]))

where list.__iadd__() succeeds but __setitem__() fails (because tuples don't
have that method).

Peter

Curious why t.__setitem__ is called. Wouldn't it still refer to the
same list?

[Peter Otten]

ca********@gmail.com wrote:

On Apr 25, 1:56 am, Peter Otten <[e-mail]:

>Aaron Brady wrote:

>>>f.func_defaults[0]
[2, 3]
f.func_defaults[0]+=[4]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
f.func_defaults[0]
[2, 3, 4]

V. interesting. Operation succeeds but with a throw. Er, raise.

This is not specific to func_defaults:

>>t = ([1],)
t[0] += [2]

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment>>t

([1, 2],)

t[0] += [2]

is resolved to

t.__setitem__(t[0].__iadd__([2]))

where list.__iadd__() succeeds but __setitem__() fails (because tuples
don't have that method).

Peter

Curious why t.__setitem__ is called. Wouldn't it still refer to the
same list?

How is Python to know? Consider

>>items = [[], 0]
items[0] += [42] # could do without __setitem__()
items[1] += 42 # __setitem__() required
items

[[42], 42]

When the item is immutable the += operation can only work by replacing it
with another value.

Peter