Python | All occurrences of substring in string
Many times while working with strings, we have problems dealing with substrings. This may include the problem of finding all positions of a particular substrings in a string. Let’s discuss certain ways in which this task can be performed.
Method #1 : Using list comprehension + startswith[]
This task can be performed using the two functionalities. The startswith function primarily performs the task of getting the starting indices of substring and list comprehension is used to iterate through the whole target string.
# Python3 code to demonstrate working of
# All occurrences of substring in string
# Using list comprehension + startswith[]
# initializing string
test_str = "GeeksforGeeks is best for Geeks"
# initializing substring
test_sub = "Geeks"
# printing original string
print["The original string is : " + test_str]
# printing substring
print["The substring to find : " + test_sub]
# using list comprehension + startswith[]
# All occurrences of substring in string
res = [i for i in range[len[test_str]] if test_str.startswith[test_sub, i]]
# printing result
print["The start indices of the substrings are : " + str[res]]
|
Output :
The original string is : GeeksforGeeks is best for Geeks
The substring to find : Geeks
The start indices of the substrings are : [0, 8, 26]
Method #2 : Using re.finditer[]
The finditer function of the regex library can help us perform the task of finding the occurrences of the substring in the target string and the start function can return the resultant index of each of them.
# Python3 code to demonstrate working of
# All occurrences of substring in string
# Using re.finditer[]
import re
# initializing string
test_str = "GeeksforGeeks is best for Geeks"
# initializing substring
test_sub = "Geeks"
# printing original string
print["The original string is : " + test_str]
# printing substring
print["The substring to find : " + test_sub]
# using re.finditer[]
# All occurrences of substring in string
res = [i.start[] for i in re.finditer[test_sub, test_str]]
# printing result
print["The start indices of the substrings are : " + str[res]]
|
Output :
The original string is : GeeksforGeeks is best for Geeks
The substring to find : Geeks
The start indices of the substrings are : [0, 8, 26]
Article Tags :
Python
Python Programs
Python string-programs
Read Full Article
Python Find All Occurrences in String
Python Python String
Created: May-01, 2021
A substring in Python is a cluster of characters that occurs within another string. Dealing with substrings can often be troublesome. One such problem is finding all the occurrences of a substring within a particular string.
This tutorial will discuss different methods to find all occurrences of a substring within a string in Python.
What is Regular Expression in Python?
A Regular Expression [RE] in a programming language is a special text string used for describing a search pattern. It is extremely useful for extracting information from text such as code, files, log, spreadsheets or even documents.
While using the Python regular expression the first thing is to recognize is that everything is essentially a character, and we are writing patterns to match a specific sequence of characters also referred as string. Ascii or latin letters are those that are on your keyboards and Unicode is used to match the foreign text. It includes digits and punctuation and all special characters like $#@!%, etc.
For instance, a Python regular expression could tell a program to search for specific text from the string and then to print out the result accordingly. Expression can include
Regular expression or RegEx in Python is denoted as RE [REs, regexes or regex pattern] are imported through re module. Python supports regular expression through libraries. RegEx in Python supports various things like Modifiers, Identifiers, and White space characters.
In this tutorial, we will learn about the Python String count[] method with the help of examples.
The count[] method returns the number of occurrences of a substring in the given string.
Example
message = 'python is popular programming language'
# number of occurrence of 'p'
print['Number of occurrence of p:', message.count['p']]
# Output: Number of occurrence of p: 4
re — Regular expression operations¶
Source code: Lib/re.py
This module provides regular expression matching operations similar to those found in Perl.
Both patterns and strings to be searched can be Unicode strings [str] as well as 8-bit strings [bytes]. However, Unicode strings and 8-bit strings cannot be mixed: that is, you cannot match a Unicode string with a byte pattern or vice-versa; similarly, when asking for a substitution, the replacement string must be of the same type as both the pattern and the search string.
Regular expressions use the backslash character ['\'] to indicate special forms or to allow special characters to be used without invoking their special meaning. This collides with Python’s usage of the same character for the same purpose in string literals; for example, to match a literal backslash, one might have to write '\\\\' as the pattern string, because the regular expression must be \\, and each backslash must be expressed as \\ inside a regular Python string literal. Also, please note that any invalid escape sequences in Python’s usage of the backslash in string literals now generate a DeprecationWarning and in the future this will become a SyntaxError. This behaviour will happen even if it is a valid escape sequence for a regular expression.
The solution is to use Python’s raw string notation for regular expression patterns; backslashes are not handled in any special way in a string literal prefixed with 'r'. So r"\n" is a two-character string containing '\' and 'n', while "\n" is a one-character string containing a newline. Usually patterns will be expressed in Python code using this raw string notation.
It is important to note that most regular expression operations are available as module-level functions and methods on compiled regular expressions. The functions are shortcuts that don’t require you to compile a regex object first, but miss some fine-tuning parameters.
See also
The third-party regex module, which has an API compatible with the standard library re module, but offers additional functionality and a more thorough Unicode support.
Which method find the list of all occurrences of the pattern in a given string?
To get all occurrences of a pattern in a given string, you can use the regular expression method re. finditer[pattern, string] . The result is an iterable of match objects—you can retrieve the indices of the match using the match.
How do you find indexOf all occurrences in a string?
“java indexof all occurrences” Code Answer’s
- String stringName = “Hello”;
- String characterToFind = “l”;
- //This example will find all the Ls in this string and will print the index of.
- //it as soon as it is detected.
-
- for[int i = 0; i < stringName. length[]; i++]{
- if[stringName. substring[i, i+1].
- System. out.
Video liên quan