Strings

Strings are sequences of characters enclosed in quotes.
(', " , ''' for multi-line strings)

print("Hello, World!")   # Output: Hello, World!

Concatenation

String concatenation or joining

fn = "Marwa"
ln = "Abubaker"
full_name = fn + " " + ln  
print(full_name)

Type Conversion/Casting

print(type(int(str(123))))

# equivalent to

a = str(123)
b = int(a)
c = type(b)
print(c)  # Output: <class 'int'>\

Escape Sequences

(\', \", \n newline, \t tab, \ backslash)

weather = "It\'s a lovely day!\nLet\'s go outside.\tEnjoy the sun."
print(weather)

Formatted Strings (f-strings)

F-strings are the preferred way for formatting.

name = "Marwa"
age = 22

print(f'Hello {name}, you are {age} years old.')                    # F-string

print('Hello ' + name + ', you are ' + str(age) + ' years old.')    # concatenated way
print("Hello {}, you are {} years old.".format(name, age))          # .format() method
print('Hello {0}, you are {1} years old.'.format(name, age))        # .format + indexing

in computer science we start counting from 0

Indexing and Slicing

language = "Python"
         #012345

# [] indexing [start:stop:stepover]

print(language[0])        # Output: P      (first character)
print(language[0:3])      # Output: Pyt    (characters from index 0 to 2)
print(language[::1])      # Output: Pto    (every character)
print(language[-1])       # Output: n      (last character)
print(language[:: -1])    # Output: nohtyP (reversed string)

Strings are immutable; slicing creates new strings.

language[0] = 'J' # This will raise an error

new_language = "J" + language[1:]  # Creating a new string
language = "J" + language[1:]      # reassigning the variable
print(language)  # Output: Jython

Common Functions/Methods used in Strings

Len Function

print(len(language))      # Output: 6 (length of the string)

quote = 'life is beautiful.'

print(quote.capitalize())   #Output: Life is beautiful. (capitalize first letter)

print(quote.upper())        # Output: LIFE IS BEAUTIFUL. (convert to uppercase)

print(quote.lower())        # Output: life is beautiful. (convert to lowercase)

print(quote.title())        # Output: Life Is Beautiful. (title case)

print(quote.find('is'))     # Output: 5 (index of first occurrence of 'is')

print(quote.replace('life', 'Life'))


print(quote)     # Original string remains unchanged its immutable