What is the difference between these two ways of appending tuples to a list

Question

I have the following code that breaks:

l = []
tup = ('a', 'b')
l = l + tup

which gives the below error

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can only concatenate list (not "tuple") to list

but the below code runs

l = []
tup = ('a','b')
l += tup

without any error.

I always thought l+= is the same as l = l +

What is going on over here?

The first operation fails because it executes `l+tup` first which calls `__add__` which isn't supported, the latter calls `__iadd__` the implementation of which allows this so they are not implemented necessarily the same — EdChum, Apr 24 '18 at 10:21

score 1 · Accepted Answer · answered Apr 24 '18 at 10:24

1

The thing is that l = l + is calling list's __add__ method, whilst l += is calling __iadd__ method, which is addition in place (equivalent to calling extend method).

answered Apr 24 '18 at 10:24

stasdeep

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What is the difference between these two ways of appending tuples to a list

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