Strings in Python

mystring = "Hello World"
print (mystring)

Hello World

#Strings in Python are arrays of bytes(charachters), the same it is presented in many programming languages like C++ & Java
for char in mystring:
    print(char)

H
e
l
l
o

W
o
r
l
d

#each charachter has its array index
print (mystring[0])

H

print (mystring[-1])

d

# get you string lenght inclus=ding spaces
print(len(mystring))

11

# check substring within the main string
if "Wo" in mystring:
    print ("Found")
else:
    print ("Not Found")

Found

# note that although "Wo" is exist, "wo" is not. search is case senstive
# check substring within the main string
if "wo" in mystring:
    print ("Found")
else:
    print ("Not Found")

Not Found

#even more you can slice a string
print (mystring[1:3])

el

# print last 5 charachters
print (mystring[-5:])

World

# a very common task to do with strings is to change its state amonge Upper-case & Lower-case
print(mystring.upper())

HELLO WORLD

print(mystring.lower())

hello world

# the "strip" method works as "trim" in other languages. 
mystring = " My Name is Mohamed Ali "
print (len(mystring), len(mystring.strip()))
#note that we have one leading space and another tail one at the end, so we have two in total to strip

24 22

# It removes white spaces from the begining and the end but NOT WITHIN a string
# if you intentionally needs to remove all within spaces that would be using join and split as following:
print (("".join(mystring.split())))

HelloWorld

#or simply by replacing each space with null-space as folloing:
print(mystring.replace(" ", ""))

HelloWorld

Now let's solve a problem from Hackerrank at https://www.hackerrank.com/challenges/swap-case/problem

def swap_case(s):
    new_string = ''
    for char in s:
        if char.isupper():
            newchar = char.lower()
        else:
            newchar = char.upper()

        new_string +=  newchar   

    return new_string

#also we may use "swapcase" function which is exactly a staright forward solution
# the solution in return would appear as concise as a "one line return statment"

def swap_case(s):

    return s.swapcase()

swap_case("Hwllo World")

'hWLLO wORLD'

Another problem from hackerRank to solve at https://www.hackerrank.com/challenges/python-string-split-and-join/problem

def split_and_join(line):
    # write your code here
    return  "-".join(line.split())

#to concatenate two strings simply use "+"
first_name = "Mohamed"
last_name = "Ali"
print ("My name is: " + first_name + ' ' + last_name )

My name is: Mohamed Ali

a similar problem from HackerRank at https://www.hackerrank.com/challenges/whats-your-name/problem

def print_full_name(first, last):
    # Write your code here
    print ("Hello " + first + ' ' + last + '! You just delved into python.')

#another solution using format would appear as folloing:
#where each "%s" refers to a varible of string that comes after "%" consequently

def print_full_name(first, last):
    # Write your code here
    print("Hello %s %s! You just delved into python." % (first,last))

print_full_name ("Mohamed", "Ali")

Hello Mohamed Ali! You just delved into python.

also, a problem from HackerRank at https://www.hackerrank.com/challenges/python-mutations/problem here the solution

def mutate_string(string, position, character):
    string_list = list(string)
    string_list[position] = character

    return ''.join(string_list)

Note that: - strings are immutable, you can not change it. Trying mystring[1] = 'M' will trigger an error - we can convert any string to new list (mutable case) where we can modify as we want - Finally, we can revert this list to its inital string state using 'join' function

#string slice can also introduce a solution to mentioned problem as folloing
def mutate_string(string, position, character):

    return  string[:position]+ character + string[position+1:]

mutate_string ('Hello world', 6, "W")
#here we mutated the lower-case 'w' with upper-case one

'Hello World'