Strings

In mathematics, variables often possess specific values such as numbers.
However, variables don’t always have to be numerical. At times, they can hold a character or a series of characters, commonly referred to as strings.
Python Programming Bootcamp: Go from zero to hero

Strings

Think of a string as a series of characters that can be indexed numerically:

Each character within a string can be accessed using its index number. Remember, collections in Python start with an index of 0.

s = "Python"
print(s)
print(s[0])

There are three ways to define strings: using single quotes (‘), double quotes (“), or triple quotes (“””).
For instance:

s = 'hello'
s = "hello"
s = """hello"""
print(s)

You can store the result of a method, like s = s.replace("world","python").

String Slices

The syntax to slice a portion of a string is:

s[ startIndex : endIndex ]

The startIndex defaults to 0 (representing the first character) if not specified. The endIndex would be the length of the string plus one.

s = "Hello Python"
print(s[0:2]) # prints "He"
print(s[2:4]) # prints "ll"
print(s[6:])  # prints "Python"

String Manipulation

There are several methods available for string manipulation:

s = "Hello Python"
print(s + ' ' + s) # concatenate two strings.
print(s.replace('Hello','Thanks')) # replace one word with another.
s = s.upper() 
print(s) # convert string to uppercase.
s = s.lower()
print(s) # convert string to lowercase.

Comparison, Search, and Concatenation

Use the operator == to compare two strings. The in keyword helps you search within a string. Plus, you can concatenate one string to another using the + operator.

sentence = "The cat is brown"
q = "cat"

if q == sentence:
    print('strings equal')
if q in sentence:
    print(q + " found in " + sentence)

Escape Characters

Python supports special characters, like ‘\n’ for a new line:

str1 = "In Python,\nyou can use escape characters in strings.\nThese characters have special meaning."
print(str1)

• \n : New Line
• \" : Double Quote
• \' : Single Quote
• \t : Tab
• \\ : Backslash

Methods for Strings

Use the following methods to manipulate strings:

• capitalize(str): Capitalizes the first letter of the string.
• count(str): Counts the frequency of the given substring.
• find(str): Finds the position of the first occurrence of a substring.
• index(str): Like find, but raises an exception if not found.
• isdecimal(): Returns true if the string is purely decimal.
• isdigit(): Returns true if the string is composed of digits only.
• isnumeric(): Returns true if the string is numeric.
• lower(): Converts the string to lowercase.
• len(str): Returns the length of the string.
• upper(): Converts the string to uppercase.
• replace(old, new): Replaces the old substring with the new one.

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