How to Substring a String in Python
String
Unicode characters collection is referred to as a String. It consists of a succession of characters, including alphanumeric and special characters.
Substring: Core Concept
A substring is a piece of a string. Python offers a variety of techniques for producing substrings, as well as for determining the index of a substring and more. Let's examine a few substring-related operations.
What is Slicing?
Slicing is a Python technique for gaining access to a subset of data from given sequences such as strings, lists, tuples, etc. A slice object is created based on a set of indices. You can choose a start index, stop index, or step-index.
Index in Python
In Python, the index starts at 0 in forwarding and -1 in reverse order.
Think about the string "String Substring" stored in a variable word.
Note: Single (' ') or double (") quotes are always used to contain strings.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
S t r i n g S u b s t r i n g
-16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1
It is evident from the above that space is likewise regarded as an index. In addition to being considered when indexing and determining a variable's length, space is also treated as a character.
Code:
String3 = "String and Substring in Python"
print (len(String3))
Output:
Python has an internal function called len() that can be used to determine a variable's length. We determined the length of the variable phrase in the aforementioned example. It is obvious that it contains spaces; therefore, when determining the variable's length, space is also considered.
- Spaces: 4
- Characters: 26
- Total: 30
Methods for Making a Substring
There are numerous ways to produce a substring. String slicing is one of the common techniques.
Depending on a certain delimiter present in a text, the split() function can produce a list of substrings.
In Python, slicing can be used to create a substring, as seen below:
string[begin: end: step]
Here,
Begin: The substring's starting index is begun. The substring contains this component. If begin is not supplied while slicing, it is considered 0.
Step: The character that must be added following the current character is called Step. If the step's default value is not specified, it is considered one.
slicing a string– Syntax:
- string [begin: end]: The substring contains characters from the start through end-1.
Example:
s= 'String and Substring.'
print(s[2:10])
Output:
- string[: end]: The substring contains characters up to end-1. An illustration of slicing without a beginning index is as follows:
Example:
s= 'String and Substring.'
print(s[:6])
Output:
- string[begin:]:characters from the starting index to the string's end are included in the substring. Example for slicing without end index:
Example:
s= "String and Substring."
print(s[1:])
Output:
- String [begin:end: step]: substring consists of characters from start to end-1, except for each step character.
Example:
s= "String and substring"
print(s[2:8:3])
Output:
- string[:]: The complete string is included. Using slicing without begin or end index.
Example:
s= " String and Substring"
print(s[:])
Output:
- string[index]: A single character is included in the substring. Giving a character at a specific index, for instance:
Example:
s= "String and Substring"
print(s[4])
Output
- Negative slicing: Get a substring by using a negative index.
Example:
s= "string and substring "
print(s[0:-4])
Output:
- Reversing a string: By employing a negative step, slicing can be utilized to return the string's reverse.
Example:
s= 'String and Substring'
print(s[::-1])
Output:
How to Create a Substring in Python
Code1:
string1= " String and Substring " # substring using slicing
st = string1[7:]
print(st)
Output:
Code2:
string2= “ string and substring “ # Creating list of substrings using split function
st = string2.split()
print(st)
Output:
How to Determine Whether a Substring is Present
To determine whether a substring is present in the provided string, use the find() method or the in operator.
Example:
string1 = 'String and Substring '
if 'Substring' in string1: # using the in Operator.
print('Substring found')
if string1.find('String') != -1: # using the find() method.
print('Substring found')
else:
print('Substring not found')
Output:
The count() Method
Use the count() method as follows to determine how many times a specific substring appears in the input string:
string3 = "using the count function "
print('Substring u count =', string3.count('u'))
Output:
Substring Indexes
There is no built-in function in Python that will find all substring indexes. However, we can define one using the find() function to get a list of all the indexes for a substring. As follows:
Code:
def indexes(string, substring):
list1 = []
length = len(string)
index = 0
while index < length:
x = string.find(substring, index)
if x == -1:
return list1
list1.append(x)
index = x + 1
return list1
st1 = "String and Substring"
print(indexes(st1, 'n')
Output:
How to Use List Slicing to Extract the Substring from a Given String
In Python, list slicing allows us to obtain the substring from a given string. Here are a few illustrations:
- Python Code to Extract a Substring From a String:
# Initialise
string1 = 'string and substring'
print ("Initial string: ", string1)
start = string1[:4] # from the start.
end = string1[2:] # from the end.
print ("Resultant substring from start:", start)
print ("Resultant substring from end:", end)
Output:
- Construct a Substring from Characters in a Specific Gap (step).
# Initialise
string2 = 'String and Substring'
print ("Initial String: ", string2)
# create substring by taking element after certain position gap and define length upto which substring is required
alt1 = string2[::3]
gap = string2[::5]
print ("Resultant substring from start:", alt1)
print ("Resultant substring from end:", gap)
Output:
- Consider a string from the middle with a small space between the characters as you create a substring.
# Initialise
string3 = 'substring in python'
print ("Initial string: ", string3)
# create substring by taking element after certain step gap in a defined length
st = string3[2:11:2]
print ("Resultant substring:", st) # Output
Output:
Conclusion
Alphanumeric and special characters are both included in Python String collections. They are also known as character arrays; the sole distinction is that they behave somewhat differently from arrays. But most of the time, strings may be thought of as arrays.
In the Python language, a substring is a group of characters with another string attached. Another name for it is "Slicing of String."
Our strings can be processed using a feature called "slicing." Slicing is a versatile technique with a wide range of applications.Different functions are available in many programming languages to extract the substring from the source or main string.