Flattening A List Or A Tuple In Python. Not Sure What The Error Is

def flatten(t): list = [] for i in t: if(type(i) != list and type(i) != tuple): list.append(i) else: list.extend(flatten(i)) ret

Solution 1:

You've assigned the built-in list to a list instance in your function, so the type check no longer works properly for list objects.

You should use a different name for the accumulator list, say, lst:

defflatten(t):
    lst = []
    for i in t:
        iftype(i) != listandtype(i) != tuple:
            lst.append(i)
        else:
            lst.extend(flatten(i))
    return lst

OTOH, you could do both checks at once using isinstance which also ensures that the objects you're running your checks against are actually types:

...
ifnotisinstance(i, (list, tuple)):
    ...

Solution 2:

You masked the name list:

list = []
...
    if(type(i) != list and ...

type(i) is never going to be equal to [].

Use a different name for your list:

result = []

You also want to use isinstance() instead of type() with equality tests:

defflatten(t):
    result = []
    for i in t:
        ifnotisinstance(i, (list, tuple)):
            result.append(i)
        else:
            result.extend(flatten(i))
    returnlist

this would have told you much earlier that you were not comparing with a type:

>>> list = []
>>> isinstance(['foo'], (list, tuple))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: isinstance() arg 2 must be a typeortuple of types

The exception is thrown because [] is not a type.

You could use a generator here to avoid the need to append or extend a new list object repeatedly. If you put the isinstance() type check outside the loop you can support non-sequences with the same function:

defflatten(t):
    ifnotisinstance(t, (list, tuple)):
        yield t
        returnfor i in t:
        yieldfrom flatten(i)

result = list(flatten(some_sequence_or_single_value))