Strings

It is an instance of str class. It is a sequence of characters. It is immutable object.

assignment

use single or double quotes to assign string. multiline strings usually tripple double quotes.

name = 'Kibria'

message = """
This is a line one.
This is line 2.
This is last line.
"""
# True multiline, line break kept

multi_line = 'This is a string' \
        'This is another string' \
        'This is yet another string'
# it looks like multiline but it is not.
# It only one string. It is for better readability.

get the length

built-in functions len() to get the length of string

name = 'Kibria'
print(len(name))
# 6

methods

There are many str methods

• upper() to convert string to uppercase
• lower() to convert string to lowercase
• capitalize() to convert first character to uppercase
• title() to convert first character of each word to uppercase
• count() to count the number of times a substring occurs in a string
• find() to find the index of a substring in a string
• replace() to replace a substring in a string with another substring
• split() to split a string into a list of substrings
• strip() to remove whitespace from both sides of a string
• rstrip() to remove whitespace from right side of a string
• lstrip() to remove whitespace from left side of a string
• isalnum() to check if all characters in a string are alphanumeric
• isalpha() to check if all characters in a string are alphabetic
• isdigit() to check if all characters in a string are digits
• islower() to check if all characters in a string are lowercase
• isupper() to check if all characters in a string are uppercase
• isspace() to check if all characters in a string are whitespaces

name = 'Kibria'

# name has all the methods of str class
name_upper = name.upper()
print(name_upper)
# KIBRIA

# does it modified the name?
print(name)
# Kibria

# No, because it is immutable hence it created new object

how to concatenation strings?

Use + operator.

You have to use type conversion explicitly.

name = 'Kibria'
age = 41
gretting = 'Hi, ' + name + '. You are ' + str(age) + ' years old.'

print(gretting)
# Hi, Kibria. You are 41 years old.

You can use f-string f"".

Use expresion inside {}. It also try to convert other types to strings automatically. It is most popular.

name = 'Kibria'
age = 41
gretting = f'Hi, {name}. You are {age} years old.'

print(gretting)
# Hi, Kibria. You are 41 years old.

You can use format methods of str class.

name = 'Kibria'
age = 41
gretting = 'Hi, {}. You are {} years old.'.format(name, age)

print(gretting)
# Hi, Kibria. You are 41 years old.

You can also do old fashion way, string interpolation.

name = 'Kibria'
age = 41
gretting = 'Hi, %s. You are %d years old.' % (name, age)

print(gretting)
# Hi, Kibria. You are 41 years old.