Python recursive function returns none. So, for instanc...

  • Python recursive function returns none. So, for instance, I In software development, recursive functions are powerful tools for solving problems that can be broken down into smaller, self-similar subproblems. Example in Python: The following code returns None on some values (eg 306, 136), on some values (42, 84), it returns the answer correctly. Calling a function produces its return value, but it's up to you to do something with that return value, whether the called function is recursive or not. Closed 3 years ago. To fix this, the recursive call should be modified to return the result of the recursive function: However, if you write a recursive function, it must return at some point (known as the "base case"), because if it doesn't it will cause infinite recursion, which will throw an exception (" Runtime Error: maximum recursion depth exceeded ") once you pass the Python interpreter's max recursion limit. The last recursive returns add (12) to the next to last which does not catch it. Behind the scenes, each recursive call adds a stack frame (containing its execution context) to the call stack until we reach the base case. The function of recursion looks simply like this: recursion_function (parameters) { // Code segments recursion_function (parameters); } Example of a recursive function returning "Undefined": Sometimes the recursive function returns undefined. The end result is "None. Dec 1, 2025 · If you’ve ever written a recursive function that appends items to a list but mysteriously returns None instead of the expected list, you’re not alone. Here is my collection: tree = { u'on 2 Before asking, I searched out some old questions and get a better idea to put the "return" in front of the inside re-invocated the function to get the expected result. upper_bound = 10 def multiples(n, multiplier, sum): print(n, multiplier, sum) add = n*multiplier + sum if n*multiplier < upper_bound: In Python, if a function finishes without executing a return <value> statement, it returns None. ---This video is based on the question return isIn(char, aStr) Without it, the function simply returns None when it terminates without seeing a return. Missing Return Statements One of the most frequent causes of a recursive function returning None is the absence of a return statement in one or more branches of the function. In Python, it’s also possible for a function to call itself! A function that calls itself is said to be recursive, and the technique of employing a recursive function is called recursion. ---This video is based on the question When do you return none in a recursive function in Python? You need to return the recursive result: otherwise the function simply ends after executing that statement, resulting in None being returned. If you’re familiar with functions in Python, then you know that it’s quite common for one function to call another. To fix this, the recursive call should be modified to return the result of the recursive function: Your All-in-One Learning Portal: GeeksforGeeks is a comprehensive educational platform that empowers learners across domains-spanning computer science and programming, school education, upskilling, commerce, software tools, competitive exams, and more. Stack Overflow | The World’s Largest Online Community for Developers I am just experimenting a little bit with Python and recursive functions. Jul 23, 2025 · Learn why Python recursive functions might return None and discover multiple practical methods, including correct return statements and iterative approaches, to resolve this common issue. I'm fairly new to Python and recursive functions as a whole, so pardon my ignorance. 0 Resolved: when l was non-empty then function was returning None so just adding a return statement resolved the issue return isIn(char, aStr) Without it, the function simply returns None when it terminates without seeing a return. If a function has no explicit return statement, Python inserts an implicit return None. . Discover why your recursive Python function is returning None and how to fix it effectively. You are catching the return from the first call, which is None. I am trying to implement a binary search tree in Python and have the following insert method (taken out of a cl Recursion is a technique in programming where a function calls itself repeatedly until it reaches a base or terminal case. This represents a parent-child relationship. Then, the stack begins to unwind as each call returns its results. Oct 7, 2013 · However, there probably does need to be a separate return statement at the end of the function, to catch when none of the filenames got matched. This blog will demystify this issue, explaining why it happens and how to fix it. Given a child, I would like to return the parent. So say you forget to declare a return statement in the body of your function/method, Python takes care of it for you then and does return None at the end of it. 1 This question already has answers here: Why does my recursive function return None? (4 answers) Discover the solution to your Python function returning `None` by understanding recursion and return values clearly explained through a practical example. For now, I wanted to write a function, which splits up a number into 4 pieces until it is smaller than 4. We’ll explore the root cause, present the correct implementation, and discuss alternative approaches, providing architectural insights for robust recursive design. In your original branch where depth > 0, you call the function but do not return its result, so each stack frame completes without a value and thus propagates None. You must return the result of the recursive call. If you ignore the return value and the calling function then ends, you end up with that calling function then returning None instead. However, the recursive call to get_input () lacks a return statement for the recursive function's return value. --- All, I have a dictionary of lists of dictionaries in Python. Here is the function: def find_path(obj, val, path=''): if isinstance(obj, dict): for k, v in Discover why a simple recursive function outputs `None` in Python and learn how to correct it for the expected results. Use return for recursive function in order to put its value into the stack , so that when function will do recursion values from the stack are taken one by one. For deeply nested data structures, a recursive function ensures no dictionary is missed regardless of nesting depth. Here is a heavily commented example that illustrates how the recursive function "unwinds" when the termination condition (the base condition) is satisfied: 1. def recurs(val): Learn how to work with recursion in your Python programs by mastering concepts such as recursive functions and recursive data structures. So, if you input the list [5, 3, 2, 4], the function should return [14, 9, 6, 4]. " Why don't the variables return properly? Non-Tail Recursion: The function does more work after the recursive call returns, so it can’t be optimized into a loop. Oct 29, 2025 · Explore why a Python recursive function returns None and examine explicit solutions using return statements to capture valid user input. The print a and return a should yield the same result, but it does not: def It is exactly the same as with a non-recursive call: if you want to propagate the return value from the function you called, you have to do that yourself, with the return keyword. 0 Resolved: when l was non-empty then function was returning None so just adding a return statement resolved the issue In the case of Python, calling a function that may raise an exception is no more difficult or unsafe than calling a function that returns a status flag and a result, but writing the function itself is much easier, with fewer places for the programmer to make a mistake. You need a return statement in the first block as well, where you make the recursive call, or else you drill down to the base case, return the length-1 list to the next level, and then return None the rest of the way up. Example in Python: Discover why a simple recursive function outputs `None` in Python and learn how to correct it for the expected results. See the examples of recursion code in Python! However, the recursive call to get_input () lacks a return statement for the recursive function's return value. It might be appropriate to raise an exception in that case (and then you'd want a try / catch around the recursion). 📌 Python Functions – Complete Concept Guide from Basics to Closures A structured reference covering Python functions, arguments, recursion, closures, and advanced parameter handling for Chapter 6: Defining functions, parameters, return values, default arguments, variable length arguments and lambda functions in Python. But when I do the same thing with my problem, it gets worse. However, managing return values in recursive functions, especially when conditional logic dictates re-calling the function, can lead to subtle yet critical errors. As such, the line var = print_hello_rec(5) is catching the returned None in the var variable, which then gets printed by print(var) Discover why your recursive Python function is returning None and how to fix it effectively. See here. When you recursively call baseConverter() don't forget that the recursive call returns the result, which you ignore, and then you execute off the end of the function, automatically returning None. In software development, recursive functions are powerful tools for solving problems that can be broken down into smaller, self-similar subproblems. 📌 Python Functions – Complete Concept Guide from Basics to Closures A structured reference covering Python functions, arguments, recursion, closures, and advanced parameter handling for Learn why Python recursive functions might return None and discover multiple practical methods, including correct return statements and iterative approaches, to resolve this common issue. One thing to keep in mind when dealing with Python functions/methods is that they always return a value no matter what. Feb 2, 2026 · Functions returning None require extra test cases to ensure None is handled correctly. Let's understand it with an example of calculating the factorial of a number n. Regardless of which method you choose, always use isinstance(x, dict) instead of type(x) == dict to correctly handle dictionary subclasses and avoid hard-to-find bugs. I've written the following code in Python, and it works fine if I put a "print" command in the recursive function to show the final value, but it won't pass its return values. However, when working with recursive functions in Python 3, you may encounter a situation where your function unexpectedly returns None instead of the expected result. In Python, the general rule is that a function always returns something. In many programming languages, if a function doesn't explicitly return a value, it implicitly returns None. In this guide, we'll address a common issue faced when writing recursive functions in Python and how to effectively solve it. some of them like: How to stop python recursion Python recursion and return statements. Recursive calls are just like any other function call; they return a result to the caller. Without a proper return, Python implicitly returns None when the function falls off the end. I can't figure out why this python function returns None if it calls itself recursively. It was part of my solution to a Project Euler problem. This article will dissect a common scenario where a recursive function for summing digits in Python returns None. I have solved the problem in a better way anyhow, but this is still annoying me as the function seems to work OK - and it seems to know the value of the variable I wanted to return. I have a function that runs over an API output and should return the path to specific key. The next to last, and all previous, return None. Because there is a case where the function returns None. The recursion enabler: Because chat() accepts a history parameter, it can be called with either a persistent history (interactive mode) or a fresh history (subagent mode). Otherwise, the base-case return path returns the results to the previous recursive call, then that recursive call does nothing with those results, so they're discarded, and None is returned automatically since you don't return anything yourself. In this article, we will explore some common reasons why this might happen and provide explanations, examples, and related evidence to help you understand and troubleshoot the issue. This code compares tail recursion and non-tail recursion using two versions of factorial function one with an accumulator (tail-recursive) and one with multiplication after recursive call (non-tail-recursive). nebsy, m9n9, eltbn, smcet, i5tbf2, nb8z8, gp3jdc, qi7zb, 7lw9s, cep6,