apt-get install to a folder of your choice

sudo apt-get install --download-only 'required-library' -o Dir::Cache::archives='path to your folder'

example path = '/home/ubuntu/test/'
example required library =  numpy 

find all the substrings in a python string

def find_subs(s):
  n = len(s)
  return [s[i:j + 1] for i in range(n) for j in range(i,n)]

Fibonacci series starting with any two numbers

def multiply(F, M):
    x = (F[0][0] * M[0][0] + F[0][1] * M[1][0])
    y = (F[0][0] * M[0][1] + F[0][1] * M[1][1])
    z = (F[1][0] * M[0][0] + F[1][1] * M[1][0])
    w = (F[1][0] * M[0][1] + F[1][1] * M[1][1])
    F[0][0] = x
    F[0][1] = y
    F[1][0] = z
    F[1][1] = w
   
def power(F, n):
    if( n == 0 or n == 1):return
    M = [[0, 1],[1, 1]] 
    power(F, n // 2)
    multiply(F, F)
    if (n % 2 != 0):
        multiply(F, M) 

def fib(a,b,n):
     
    F = [[0, 1],[1, 1]]
    if (n == 0): return a
    if (n == 1): return b
    power(F, n - 1)
         
    return F[0][1]*a + F[1] [1]*b

How to initialize dynamic variables

Example 1:

 

Example 2 :
 

str[i] = malloc(len(char)*5)

Why lowercase variable is used other than uppercase?

Practically speaking variables should be allowed in any case, but just to follow convention in a particular domain we use certain format of words.
For example Class-names usually start with  UPPERCASE and if you want to use same name for object it can be only possible by using lowercase.

python remove text from string after character(s) without using regex

pivot = '...'
required = text.split(pivot, 1)[0]