## Recursion sequences python

how can I print all sequences of length n containing letters from a list (that can repeat themselves)? **using recursion**.
for example:

seq = ['a', 'b'] n = 2

output:

aa,ab,ba,bb

I've been looking up and could only find recursive programs that give all sequences with **no** repetition. furthermore, I couldn't find any solution regarding a given list (most of them are given strings)

one of the problems is that I'm not sure how to address the function recursively while it contains the length n.

You can recruse on `n`

, the length of the subsequence. If `n == 0`

, there is only one subsequence - the empty one. Otherwise, you take all pairs of elements of your list and subsequences of length n-1, and get all subsequences of length `n`

.

def subseqs(lst, n): if n <= 0: return [[]] else: return [[x] + xs for x in lst for xs in subseqs(lst, n - 1)]

**Python Tutorial: Recursive Functions,** Introduction into recursive thinking, recursion and recursive functions in The Fibonacci numbers are the numbers of the following sequence of integer values:. Python Recursion Function Example. 2. Fibonacci Series. The Fibonacci series is the sequence of numbers where each number is the sum of two preceding numbers. For example – 1, 1, 2, 3, 5, 8, 13, 21 and so on. Let’s look at a function to return Fibonacci series numbers using loops.

##### One of the ways to solve this is to use `itertools.product`

import itertools seq = ['a', 'b'] n = 2 for a, b in itertools.product(seq,repeat = n): print (f"{a}{b}") #loop through all the products and print them #result --> # aa # ab # ba # bb

I hope this helps :)

**Thinking Recursively in Python – Real Python,** Learn how to work with recursion in your Python programs by mastering concepts such as recursive functions and recursive data structures. The need for donations Bernd Klein on Facebook Search this website: This topic in German / Deutsche Übersetzung: Rekursion und Rekursive Funktionen Python 3 This is a tutorial in Python3, but this chapter of our course is available in a version for Python 2.x as well: Recursive Functions in Python 2.x

I will use itertools

import itertools seq = ['a', 'b'] n = 2 print([i+j for i,j in itertools.product(seq,repeat=n)])

This is a task for product ;)

BTW: if you don’t want modules look at source code:

def product(*args, repeat=1): # product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy # product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111 pools = [tuple(pool) for pool in args] * repeat result = [[]] for pool in pools: result = [x+[y] for x in result for y in pool] for prod in result: yield tuple(prod)

Source code at: https://docs.python.org/3/library/itertools.html#itertools.product

Learn and Reverse engineering it to fit your need ;). Example if you don’t want it to return tuples.

**Recursion sequences python,** You can recruse on n , the length of the subsequence. If n == 0 , there is only one subsequence - the empty one. Otherwise, you take all pairs of In Python, a function is recursive if it calls itself and has a termination condition. Why a termination condition? To stop the function from calling itself ad infinity.

Here is another approach, using only recursion. The `findSeqRecPerChar`

finds all possible combinations for a specific character in the list and the `findSeqRec`

find all possible combinations for every character:

seq = ['a', 'b'] n = 2 def findSeqRecPerChar(seq,n,elem,index): if index == n: return [] else: return [elem+seq[index]] + findSeqRecPerChar(seq,n,elem,index+1) def findSeqRec(seq,n,index,l): if index == n-1: return l + [] else: l.extend(findSeqRecPerChar(seq,n,seq[index-1],0)) return findSeqRec(seq,n,index+1,l) result = findSeqRec(seq,n,-1,[]) print(result)

Output:

['aa', 'ab', 'ba', 'bb']

**Understanding Recursive Functions with Python,** Understanding Recursive Functions with Python. By Marcus This sequence makes an assumption that Fibonacci numbers for 0 and 1 are also 0 and 1. Python Program to Generate a Fibonacci Sequence Using Recursion Get the length of the Fibonacci series as input from the user and keep it inside a variable. Send the length as a parameter to our recursive method which we named as the gen_seq (). The function first checks if the length is lesser than

**Python Recursion (Recursive Function),** Recursive functions make the code look clean and elegant. A complex task can be broken down into simpler sub-problems using recursion. Sequence generation Generally we can say: Recursion in computer science is a method where the solution to a problem is based on solving smaller instances of the same problem. Recursive Functions in Python Now we come to implement the factorial in Python. It's as easy and elegant as the mathematical definition.

**11. Recursion and exceptions,** Now suppose our job is to write a function that will sum all of the values in a nested number list. Python has a built-in function which finds the sum of a sequence 7 Ways to Create Sequences in Python For, Iters, Recursion, Maps, Etc. Background. A sequence in mathematics, is a collection (like a set) of mathematical objects where the order of the objects is significant, and duplicate members of the collection are allowed. In computer science, we represent sequences as arrays, lists, streams, and a

**Python Recursion Example - Recursive Functions,** Python recursion examples for Fibonacci series and factorial of a number. The Fibonacci series is the sequence of numbers where each number is the sum of The recursion exits when n < 0, given that we're only printing, there's nothing left to be done afterwards and it's ok to return None (Python's default return value)