Why Python Recursive Function Returns 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 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.

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

Python recursive function returns None instead of value

You did not return any value from your recursive call break_up_number_into_fours(full_result) , you need to do it like:

def break_up_number_into_fours(input):
    flag = 0
    input_list = []
    full_result = []
    if isinstance(input, list):
        input_list.extend(input)
    else:
        input_list.append(input)

    for item in input_list:
        if item > 4:
            result = [item/4]*4
            full_result.extend(result)
            flag = 1
        else:
            full_result.append(item)

    if flag == 1:

        return break_up_number_into_fours(full_result) // here you need to return the value in respective recursive call
    else:
        print(full_result)
        return full_result

test = break_up_number_into_fours(20)

print(test)

Output:

[1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25]

[1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25, 1.25]

Python recursive Function returns extra 'None' once complete

This is not a recursion problem. In the end, if results != []: you print something and return results. Else your function just ends and returns nothing. But in python, if your append the value of function that returned nothing - you get None. So when your result is left empty - you are getting None.

You can either check what you are appending or pop() if you got None after appending.