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python tricks.md

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Convert to int, float

int() or float()

Convert to string

str()

Split a string to characters

list("Hello")

Add to, remove from list

n = []  
n.append(3)  
n.append(4)  
n.pop(0) ## index position  
n.remove(4) ## actual value

Accept list of comma separated integers

n = [int(i) for i in input().split(',')]

Split a number into corresponding digits

arr = [int(i) for i in list(str(24869453))]

Remove duplicates from list

l = list(set(l))

Reverse a list

L = L[::-1]

Copy a list

arrcpy = arr[:]

Print upto 6 decimal places

print('{0:.6f}')

Find max of a list below a maximum limit

max([i for i in m if i <= 2]) ## finds max number of list m below 2

Use global variable

def fun1():  
  global s  
  s = "Hello"  

def fun2():  
  print(s)

Convert decimal number to any other base

def findToBase(num, base):  

  if num == 0:  
    return 0  

  if num < base:  
    r = num  
  else:  
    r = num % base  

  return int(str(findToBase(int(num/base), base)) + str(r))

nCr in list

def get_nCr(r, arr):  
    nCr = []  
    if r == 1:  
        for i in arr:  
            nCr.append([i])  
    elif r > 1:  
        n = len(arr)  
        for i in range(n-r+1):  
            a = arr[i]  
            last = get_nCr(r-1, arr[i+1:])  
            element = []  
            for l in last:  
                l = [a] + l  
                if l not in nCr and l not in element: element.append(l)  
            nCr += element  

    return nCr

find lcm of a list

from math import gcd  
def getLCM(arr):  

  LCM = arr[0]  
  for i in arr[1:]:  
    LCM = LCM*i/gcd(int(LCM),i)  

  return LCM

Magic 3*3 matrix possible cases

[
[[8, 1, 6], [3, 5, 7], [4, 9, 2]],
[[6, 1, 8], [7, 5, 3], [2, 9, 4]],
[[4, 9, 2], [3, 5, 7], [8, 1, 6]],
[[2, 9, 4], [7, 5, 3], [6, 1, 8]],
[[8, 3, 4], [1, 5, 9], [6, 7, 2]],
[[4, 3, 8], [9, 5, 1], [2, 7, 6]],
[[6, 7, 2], [1, 5, 9], [8, 3, 4]],
[[2, 7, 6], [9, 5, 1], [4, 3, 8]],]

(https://www.hackerrank.com/challenges/magic-square-forming/problem)[https://www.hackerrank.com/challenges/magic-square-forming/problem]

Recursive way to get list of all subsets which sum up to a specific number

def main():  
    global all  
    all = []  
    subsetSum(6, [1,2,3,4,5,3])  
    print(all)  

def subsetSum(m, l):  
    if (len(l) == 0):  
        return  
    if (sum(l) == m and l not in all):  
        all.append(l)  
    for i in range(len(l)):  
        subsetSum(m, l[:i] + l[i+1:])  
        
if __name__ == '__main__':  
    main()

Gives output: [[3, 3], [2, 4], [1, 5], [1, 2, 3]]