a = []; a += 'abc' versus a = a+'abc'

Asked Jan 23 '20 at 13:56

Active Jan 23 '20 at 14:00

Viewed 39 times

I understand that you cannot concatenate a list and a string. So it makes sense that a=a+'abc' throws an exception "TypeError: can only concatenate list (not "str") to list".

But why does a+='abc' result in a == ['a','b','c']?

I thought a = a+b and a+=b should always give the same result.

edited Jan 23 '20 at 14:00

John Kugelman

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asked Jan 23 '20 at 13:56

tony ladd

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`+=` is like calling `a.extend()` – Chris_Rands Jan 23 '20 at 14:00
see for example https://stackoverflow.com/questions/2347265/why-does-behave-unexpectedly-on-lists#comment78372641_2347423 and the next answer – Chris_Rands Jan 23 '20 at 14:01
In *general*, a = a+b and a+=b are not equivalent – juanpa.arrivillaga Jan 23 '20 at 14:05
`+=` takes another *iterable* and adds all its items to the list. `+` concatenates *two lists*. – deceze Jan 23 '20 at 14:05

a = []; a += 'abc' versus a = a+'abc'

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