Why Does My Recursive Function Return None

Recursive function returning none in Python

You need to return the recursive result:

else:
   return get_path(directory[filename], rqfile, path)

otherwise the function simply ends after executing that statement, resulting in None being returned.

You probably want to drop the else: and always return at the end:

for filename in dictionary.keys():
    path = prefix+[filename]
    if not isinstance(dictionary[filename], dict):

        if rqfile in str(os.path.join(*path)):
            return str(os.path.join(*path))

    return get_path(directory[filename], rqfile, path)

because if rqfile in str(os.path.join(*path)) is False then you end your function without a return as well. If recursing in that case is not the right option, but returning None is not, you need to handle that edgecase too.

Recursive function returning none?

You are ignoring the return values of recursive calls. You need to explicitly return those too:

elif input[mid] > target:
    return bisect(input[:mid], target)
elif input[mid] <= target:
    return bisect(input[mid:], target)

Recursive calls are just like any other function call; they return a result to the caller. If you ignore the return value and the calling function then ends, you end up with that calling function then returning None instead.

Why is my recursive function returning a None value

As you go down the call stack, you need to be returning values back up the stack once you hit the base case.

def detectNumber(stringVal, lp, makeNumber=""):
    try:
        if stringVal[lp] == " ":

            print("Space detected")

            print(f"At start makeNumber was {makeNumber}")
            return makeNumber

        else:
            makeNumber += stringVal[lp]
            lp += 1
            # Here
            return detectNumber(stringVal, lp, makeNumber=makeNumber)

    except:
        print(f"Error {lp}")

>>> detectNumber('123 ', 0)
Space detected
At start makeNumber was 123
'123'

You were getting None, because the value was only returned to the last recursive caller, rather than all the way back up the stack

recursive function returning 'None'

Change it please to

def fib(n):
    nums.append(nums[-1] + nums[-2])
    if len(nums) - 1 != n:
        return fib(n)
    elif len(nums) - 1 == n:
        return nums

Recursive function return None even though print() works

You need to return count_lowercase(s, low + 1, high), otherwise the function simply ends after executing that statement, resulting in None being returned.

count = 0


def count_lowercase(s, low, high):
    global count
    if low > high:
        return count
    else:
        if s[low] == s[low].lower():
            count += 1
        return count_lowercase(s, low + 1, high)

Why Recursive function return None

The return statement is missing!

Do this:

def good(num,sum):

    if num == 0:
        return sum
    sum = sum + num
    num = num - 1
    return good(num, sum)

This is because the function is called but is not returning the new values recursively.

One of the best website that explains this in depth and clearly is realpython.com, have a look especially at: maintaining-state but I suggest you to have a look at the whole article.

For sake of completeness I quote a section where I think is related to the issue you encountered:

Behind the scenes, each recursive call adds a stack frame (containing its execution context) to the call stack until we reach the base case. Then, the stack begins to unwind as each call returns its results.

• unwind: Basically it returns it backward.

When dealing with recursive functions, keep in mind that each recursive call has its own execution context.

Other Stack Overflow Related questions

• recursive-function-returning-none-in-python
• python-recursion-with-list-returns-none
• i-expect-true-but-get-none

Why does my recursive function return None?

It is returning None because when you recursively call it:

if my_var != "a" and my_var != "b":
    print('You didn\'t type "a" or "b". Try again.')
    get_input()

..you don't return the value.

So while the recursion does happen, the return value gets discarded, and then you fall off the end of the function. Falling off the end of the function means that python implicitly returns None, just like this:

>>> def f(x):
...     pass
>>> print(f(20))
None

So, instead of just calling get_input() in your if statement, you need to return it:

if my_var != "a" and my_var != "b":
    print('You didn\'t type "a" or "b". Try again.')
    return get_input()

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