如何在Python中计算位数的平均值

Question

I have a assignment for my computer class, and the one of the question asked us to write a code which will calculate the average of the digits until it gets to a letter (alphabet).

This was the description:

This function receives as input one string containing digits or letters. The function should return one float number contaning the average calculated considering all the digits in the string starting from the first position in the string and considering all digits until one letter is found or until reaching the end of the string. If there are no digits the function should return the value 0.0 .

So I came up with the following code:

def avgUntilLetter (st):
    digits1 = [int(x) for x in st if x.isdigit()]
    total = sum(digits1)
    if digits1:
        avg = float(total) / len(digits1)
        return avg
    if st.isalpha():
        return 0.0

For answer, for example, I should get 2.0 as return value if the CodeWrite put in avgUntilLetter('123a456') . I'm getting the average of all digits, what do I need to put in to my code to fix this?

Answer 1

You are taking all digits, not just the ones at the start. You need to stop calculating when you encounter the first non-digit.

This is easiest if you just loop over all characters one by one and break out when you reach the first non-digit:

def avgUntilLetter(st):
    total = count = 0
    for x in st:
        if not x.isdigit():
            break
        count += 1
        total += int(x)
    if not count:
        return 0.0
    return float(total) / count

Here count tracks how many digits we found at the start; if it is still 0 no digits were found.

Demo:

>>> def avgUntilLetter(st):
...     total = count = 0
...     for x in st:
...         if not x.isdigit():
...             break
...         count += 1
...         total += int(x)
...     if not count:
...         return 0.0
...     return float(total) / count
... 
>>> avgUntilLetter('123a456')
2.0