Python Strings

Python string is a sequence of characters enclosed within quotation marks that is used to represent text data in a program.

In this chapter, you will learn what a string is in Python, how strings are created, and how Python treats characters and text data.

What is a String in Python?

A string in Python is a sequence of characters enclosed within quotation marks.

It can include letters, numbers, symbols, and even whitespace characters. Python does not have a separate character data type, so even a single character is treated as a string of length 1.

For example, "welcome" is a string consisting of a sequence of characters such as 'w', 'e', 'l', 'c', 'o', 'm', 'e'.

Example

Let us see an example of strings in Python.

Output:

String: tpointtech  
Data Type:   

Explanation:

In this example, the sample_str holds the value "tpointtech" and is defined as a string.

Characteristics of Python Strings

Here are some characteristics of strings in Python:

• Immutable: Once a string is created, we cannot change it. Any operation in terms of modifying a string will actually make a new string.
• Ordered: Strings are ordered collections of characters where each character has a fixed index (starting from 0). We can access the characters using their position.
• Iterable: We can iterate through each character of a string using Python loops, like for and while.
• Support Slicing: We can slice a string to extract substrings with the help of [start : end] syntax.
• Unicode Support: By default, strings in Python 3 are stored as Unicode. This allows us to handle international languages and emojis efficiently.
• Dynamic Length: We can initialize a string of any length, from an empty string to a string consisting of millions of characters.
• Can contain any characters: A string can include letters (A-Z, a-z), digits (0-9), special characters like @, #, $, %, etc., spaces, tabs, and even newlines.

Creating a String

We can create strings using either single quotation marks ('…') or double quotation marks ("…").

Example

Let us see an example showing both ways of creating strings in Python.

Output:

String 1: Welcome to Tpoint Tech
String 2: Welcome to Tpoint Tech

Explanation:

In the above example, we have created strings using single and double quotation marks. These quotation marks can be interchangeably utilized while initializing a string.

Creating Multiline Strings

In case we want a string to span multiple lines, then we can make use of triple quotation marks ('''…''' or """…""").

Example

The following is a simple example of how to create a multiline string in Python.

Output:

Multiline String 1:
Learning Python 
is fun with 
Tpoint Tech

Multiline String 2:
Tpoint Tech is
the best place to learn
Python Programming

Explanation:

In the above example, we have created multiline strings using triple quotation marks.

Accessing Characters in a String

In Python, strings are sequences of characters that can be accessed individually with the help of indexing. Strings are indexed 0 from the start and -1 from the end. This indexing helps us retrieve particular characters from the string effortlessly.

Example

Here is an example to access a specific character in a given string:

Output:

Given String: Tpoint Tech
s[0] = T
s[9] = c

Explanation:

In the above example, we have used indexing to access the different characters in the given string.

Note: Accessing an index out of range will result in an IndexError exception. Moreover, only integers are allowed as indices, and using other types like float, string, or Boolean will result in a TypeError exception.

Accessing String with Negative Indexing

In Python, we are allowed to use negative address references in order to access the characters from the back of the string. For example, -1 refers to the last character, -2 refers to the second last, and so on.

Example

Let us take a look at an example showing how to access characters in a string using negative indexing.

Output:

Given String: Tpoint Tech
s[-1] = h
s[-6] = t

Explanation:

In the above example, we have used negative indexing to access the characters from the back of the given strings.

String Slicing

Slicing is a way in Python that allows us to extract a portion of a string by specifying the start and end indexes. The format for slicing a string is string_name[start : end], where the start is the index where slicing begins, and the end is the index where it ends.

Example

The following is an example showing the implementation of string slicing in Python.

Output:

Given String: Tpoint Tech
s[1:5] = poin
s[:4] = Tpoi
s[4:] = nt Tech
s[::-1] = hceT tniopT

Explanation:

In this example, we have accessed the range of characters in the given string using slicing.

String Immutability

String in Python is an immutable data type that cannot be changed after creation. However, we can manipulate strings using various methods like slicing, concatenation, or formatting in order to create new strings on the basis of the original one.

Example

Let us take a look at an example showing how to manipulate a string in Python.

Output:

Given String: tpointtech
New String: Tpoint Tech

Explanation:

In the above example, we can observe that we cannot directly modify the character in the given string due to string immutability. However, we have created a new string by manipulating the given string by performing formatting, concatenation, and slicing.

Deleting a String

Since Python strings are immutable, we can't delete individual characters from a string. However, Python provides accessibility to delete an entire string variable using the del keyword.

Example

Let us take an example to demonstrate how to delete a string.

Output:

NameError: name 'msg' is not defined

Explanation:

In the above example, we have used the del keyword to delete the given string variable. As we can observe, the program is raising a NameError exception when we try calling it after deletion.

Updating a String

A string is an immutable data type which cannot be modified. However, we can update a part of a string by creating a new string itself.

Example

Let us see an example to understand how to update a string in Python.

Output:

Given String: welcome learners
New String 1: Welcome learners
New String 2: welcome to Tpoint Tech

Explanation:

In the first case, we have sliced the original string given_str from index 1 to end and concatenate it with "W" in order to create a new update string new_str_1.

For the second case, we have created a new string as new_str_2 and used the replace() method to replace "learners" with "to Tpoint Tech".

Common String Methods

Python offers many built-in methods for string manipulation. These methods allow us to determine the length of a string, change its cases, validate it, split and join it, search and find substrings, and a lot more. Below are some of the most useful methods:

len()

The len() function is used to determine the length of a string. This function returns the total number of characters in a given string.

Example

The following example shows the usage of the Python len() function:

Output:

Given String: tpointtech
Number of Characters: 10

Explanation:

In this example, we have used the len() function and determined the number of characters in the given string.

upper() and lower()

In Python, the upper() method is used to convert all the characters of the string to uppercase. Whereas, the lower() method allows us to convert all the characters of the string to lowercase.

Example

The following example displays the use of the String upper() and lower() methods in Python:

Output:

Given String: Tpoint Tech
Uppercase String: TPOINT TECH
Lowercase String: tpoint tech

Explanation:

In this example, we have used the upper() method to change the case of the given string to uppercase. We have also used the lower() method to change the case to lowercase.

Note: Strings are immutable; therefore, all of these methods will return a new string, keeping the original one unchanged.

strip() and replace()

The strip() method allows us to remove the leading and trailing whitespaces from the string. The replace() method is used to replace all occurrences of a particular substring with another.

Example

Let us take a look at an example to understand the implementation of the strip() and replace() methods in Python.

Output:

String 1:       TpointTech    
After removing spaces from both ends:
TpointTech
String 2: Learning Python with TpointTech is fun!
After replacing 'fun' with 'amazing':
Learning Python with TpointTech is amazing!

Explanation:

In the first case, we have used the strip() method to remove the leading and trailing spaces from the given string.

In the second case, we have used the replace() method to replace 'fun' with 'amazing' in the given string.

To learn more about string methods, refer to Python String Methods.

String Concatenation and Repetition

Python allows us to concatenate and repeat strings using different operators. We can concatenate strings with the help of the '+' operator and repeat them using the '*' operator.

Example

The following example shows the use of these two operations:

Output:

Concatenated String: Tpoint Tech
Repeated String: TpointTpointTpointTpoint

Explanation:

In the above example, we have used the + operator to concatenate the strings to create a new string. We have also used the * operator to repeat the specified string multiple times.

Formatting Strings

There are several ways in Python that allow us to include variables inside strings. Some of these methods are discussed below:

Using f-strings

The convenient and most desirable method to format strings in Python is by using f-strings.

Example

Let us take a look at the following example:

Output:

John is a 19 years old boy living in New York.

Explanation:

In the above example, we have included the given variables to a string using the f-string.

Using format()

The format() method is another way to format strings in Python.

Example

Let us take a look at a simple example showing the use of the format() method in Python.

Output:

Sachin is a Software Developer at Apple Inc.

Explanation:

In the above example, we have used the format() method to include the specified variables in a string.

String Membership Test

We can test whether a substring exists within a string or not using the 'in' and 'not in' keywords.

Example

The example of these keywords is shown below:

Output:

Does 'p' exist in 'Tpoint Tech'? True
Does 'a' exist in 'Tpoint Tech'? False
Does 'e' not exist in 'Tpoint Tech'? False
Does 'g' not exist in 'Tpoint Tech'? True

Explanation:

In the above example, we have checked if the specified substrings is a part or member of the given string using the 'in' and 'not in' keywords.