Strings in Python

Overview:

Strings are used for representing and processing texts of arbitrary length.
In other programming languages like C, C++ and Java there is a separate type representing characters. In those languages strings are collection of characters.
In Python there is no separate type to represent characters.
Python strings are a collection of code points.
In Python, individual characters as well, are represented as strings.
Strings are immutable in Python.
Strings in Python are of type str which is a built-in class in Python.

String Construction:

Strings literals can be constructed in multiple ways using:

Single quotes
Double quotes
Triple quotes
Constructor

Single Quoted Python Strings Vs Double Quoted Python Strings:

In Python, there is no difference between strings constructed using single quotes and double quotes. It is good if the developer could stick to one convention.

If a string contains a single quote or double quote - use the other one to avoid escaping it with a backslash, which improves readability.

Triple Quoted Strings:

Triple quoted strings are used to provide string literals that span across multiple lines in a Python Program. All the white spaces are taken as part of the string literal. Triple quoted strings are also used as docstrings in a Python Program.

Using str constructor:

The str constructor function takes a collection of unicode points(ie., characters) enclosed by single/double/triple quotes.

Another variant of the str() constructor takes encoding and the error handling scheme as parameters to it.

Example:

sampleString = str("Universe is Big")

# Convert the string to lower case

lowerCase = sampleString.lower()

print("String converted to lower case:{}".format(lowerCase))

# Capitalize only the first letter

capitalized = sampleString.capitalize()

print("String with first letter capitalized:{}".format(capitalized))

# Find the length of the string

stringLength = len(sampleString)

print("String length:{}".format(stringLength))

# Check if all the characters all alphabets

alphaCheck = sampleString.isalpha()

# False as the string has space characters

print("All the characters all alphabets:{}".format(alphaCheck))

Output:

String converted to lower case:universe is big

String with first letter capitalized:Universe is big

String length:15

All the characters all alphabets:False

String Methods:

The str class in Python provides a collection of methods to process strings. The str methods are listed here as a table.

Method Name	Responsibility
capitalize()	Returns a copy of the string instance with the following modifications done Capitalize the first character Make all the other characters as lower case
casefold()	Returns a copy of the string, which is casefolded. Casefolding is a more aggressive form of lowercasing.
center(width[, fillchar])	This method does not return the central character or any central part of the string. On a string with “n” as length, center() will make the original string appear in the center portion. Remaining portion of the string will be padded with specified padding character.
count(sub[, start[, end]])	Returns the number of times a substring appears in a given string object.
encode(encoding="utf-8", errors="strict")	Returns a byte array corresponding to the characters (i.e., codepoints) Present in the string.
endswith(suffix[, start[, end]])	endswith() returns True if a string ends with the specified suffix and returns False otherwise. A list of strings from a tuple as well could be provided as parameter instead of a single string. endswith() accepts start and stop position for the search.
find(sub[, start[, end]])	In a given string object, find() returns the lowest position of a specified substring.
index(sub[, start[, end]])	The index() method returns the lowest position at which a substring is found. Raises a ValueError otherwise.
isalnum()	isalnum() checks whether a string is absolutely aplhanumeric, meaning if any non-alphanumeric characters found will return false. Will return true only if the whole string is made of digits and alphabets.
isalpha()	The isalpha() method returns true if a string object is solely made of alphabets; returns false otherwise; isalpha() returns false for empty strings.
isidentifier()	The isidentifier() method returns True if the string contents form a valid python identfier name; returns False otherwise.
islower()	islower() method will return True if all the characters in a string object are lower cased. islower() returns False if at least one character present in the string is not lower cased. If a string is an empty string, islower() retruns false.