简单的 Python 代码段/错误

Question

He defines the following Python function normally:

def findMax (team, board, MIN, MAX, levels)
    ...
    ...
    return

In his program he calls it this way:

myValue = findMax(team, board, MIN, MAX, 3) [1]

and it works properly. But if I remove the bracketed 1 and call it like this:

myValue = findMax(team, board, MIN, MAX, 3)

it throws this error:

TypeError: list indices must be integers or slices, not tuple.

My question is this: What is the bracketed 1 doing? I have never seen a bracketed number following arguments in a called function and I can't find the answer anywhere in the Python literature.

Answer 1

[1] is a subscription expression . findMax() returns a list , and [1] picks out a single element from that sequence, the one with index 1.

When you remove the [1] expression, you get the TypeError later on when code that expected a different type of object, but is now given that list instead.

Perhaps you found the space between the ) of the findMax() call and the [1] confusing. It is much better to leave out that space, and the Python style guide states no spaces should be used there, but spaces are perfectly legal there:

>>> l = ['foo', 'bar']
>>> l[1]
'bar'
>>> l [1]
'bar'
>>> l             [1]
'bar'

Legal, but confusing to new coders.