Strings

Python Strings are Immutable objects that cannot change their values.

>>> str1 = "strings are immutable!"
>>> str1[0] = "S"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment

You can update an existing string by (re)assigning a variable to another string.

Python does not support a character type; these are treated as strings of length one.

Python accepts single ('), double (") and triple (''' or """) quotes to denote string literals.

str1 = 'str1' 
str2 = '''str2''' 
str3 = "str3"
str4 = """str4"""

String indexes starting at 0 in the beginning of the string and working their way from -1 at the end of string.

positive indexes    >>      | 0 | 1 | 2 | 3 | 4 |
string is 'HELLO'   >>      | H | E | L | L | O |
negative indexes    >>      |-5 |-4 |-3 |-2 |-1 |

String formatting

>>> num = 6
>>> string = "I have {} books!".format(num)
>>> print(string)
I have 6 books!

Common String Operators, Assume: a='Hello' and b='Python'

Operator	Description	Example
`+`	Concatenation - Adds values on either side of the operator	`a+b >>> HelloPython`
`*`	Repetition - Creates new strings, concatenating multiple copies of the same string	`a*2 >>> HelloHello`
`[]`	Slice - Gives the character from the given index	`a[1] >>> e` `a[-1] >>> o`
`[:]`	Range Slice - Gives the characters from the given range	`a[1:4] >>> ell`
`in`	Membership - Returns true if a character exists in the given string	`'H' in a >>> True`

Common String Methods

Method	Description
`str.count(sub, beg=0, end=len(str))`	Counts how many times sub occurs in string or in a substring of string if starting index beg and ending index end are given.
`str.isalpha()`	Returns `True` if string has at least 1 character and all characters are alphanumeric and `False` otherwise.
`str.isdigit()`	Returns `True` if string contains only digits and `False` otherwise.
`str.lower()`	Converts letters in string to lowercase.
`str.upper()`	Converts letters in string to uppercase.
`str.replace(old, new)`	Replaces all occurrences of old in string with new.
`str.split(str=' ')`	Splits string according to delimiter `str` (space if not provided) and returns list of substrings.
`str.strip()`	Removes all leading and trailing white spaces of string.
`str.title()`	Returns "titlecased" version of string.

Common String Functions

Function	Description
`str(x)`	To convert `x` to an String
`len(x)`	Gives the total length of the string