Python for loop: iteration not complete

Your function terminates after the first loop, because you have an unconditional return inside that loop. Move the return to the outside of the loop.

def measure(p):
    for x in range(len(p)):
        if p[x][0] == 'U':
            p[x] = 1
        else:
            p[x] = 0
    return p

print measure(['Dave','Sebastian','Katy'])
print measure(['Umika','Umberto'])

Result:

[0, 0, 0]
[1, 1]

Know that return always terminates a function when executed. In the first loop of your for loop, your function executes the return statement and end the function measure. That's why only the first element of p is changed to 0 or 1.

Just put the return statement outside the for loop

def measure(p):
    for x in range(len(p)):
        if p[x][0] == 'U':
            p[x] = 1
        else:
            p[x] = 0
    return p

As a bonus, your function is quite simple, and can be made in a one-liner as follow:

def f(L):
    return [1 if elt[0].lower() == "u" else 0 for elt in L]

f(['Umika','Umberto'])
Out[27]: [1, 1]

f(['Dave','Sebastian','Katy'])
Out[28]: [0, 0, 0]

The identation of the return statement is inside the for loop. That means the code stops after modifying only the first element.

Put the return statement at the same identation level as the for statement and it should work.

Your return statement is indented too far - that's why it is stopping after the first element. It should be indented at the same level as the for x... line. Try:

>>> def measure(p):
...     for x in range(len(p)):
...         if p[x][0] == 'U':
...             p[x] = 1
...         else:
...             p[x] = 0
...     return p
...
>>> print measure(['Dave','Sebastian','Katy'])
[0, 0, 0]
>>> print measure(['Umika','Umberto'])
[1, 1]