import re
Example:
import re
txt = "The rain in Spain"
x = re.search("^The.*Spain$", txt)
# Search the string to see if it starts with "The" and ends with "Spain"
| Function | Description |
|---|---|
| findall | Returns a list containing all matches |
| search | Returns a Match object if there is a match anywhere in the string |
| split | Returns a list where the string has been split at each match |
| sub | Replaces one or many matches with a string |
Metacharacters are characters with a special meaning.
| Character | Description | Example |
|---|---|---|
| [] | A set of characters | “[a-m]” |
| \ | Signals a special sequence (can also be used to escape special characters) | “\d” |
| . | Any character (except newline character) | “he..o” |
| ^ | Starts with | “^hello” |
| $ | Ends with | “world$” |
| * | Zero or more occurrences | “aix*” |
| + | One or more occurrences | “aix+” |
| {} | Exactly the specified number of occurrences | “al{2}” |
| | | Either or | “falls|stays” |
| () | Capture and group |
A special sequence is a \ followed by one of the characters in the list below, and has a special meaning:
| Character | Description | Example |
|---|---|---|
| \A | Returns a match if the specified characters are at the beginning of the string | “\AThe” |
| \b | Returns a match where the specified characters are at the beginning or at the end of a word | r”\bain” r”ain\b” |
| \B | Returns a match where the specified characters are present, but NOT at the beginning (or at the end) of a word | r”\Bain” r”ain\B” |
| \d | Returns a match where the string contains digits (numbers from 0-9) | “\d” |
| \D | Returns a match where the string DOES NOT contain digits | “\D” |
| \s | Returns a match where the string contains a white space character | “\s” |
| \S | Returns a match where the string DOES NOT contain a white space character | “\S” |
| \w | Returns a match where the string contains any word characters (characters from a to Z, digits from 0-9, and the underscore _ character) | “\w” |
| \W | Returns a match where the string DOES NOT contain any word characters | “\W” |
| \Z | Returns a match if the specified characters are at the end of the string | “Spain\Z” |
A set is a set of characters inside a pair of square brackets ` []` with a special meaning:
| Set | Description |
| ———– | ———————————————————— |
| [arn] | Returns a match where one of the specified characters (a, r, or n) are present |
| [a-n] | Returns a match for any lower case character, alphabetically between a and n |
| [^arn] | Returns a match for any character EXCEPT a, r, and n |
| [0123] | Returns a match where any of the specified digits (0, 1, 2, or ` 3) are present |
| [0-9] | Returns a match for any digit between 0 and 9 |
| [0-5]\[0-9] | Returns a match for any two-digit numbers from 00 and 59 |
| [a-zA-Z] | Returns a match for any character alphabetically between a and z, lower case OR upper case |
| [+] | In sets, +, *, ., |, (), $,{} has no special meaning, so [+] means: return a match for any +` character in the string |
The findall() function returns a list containing all matches.
Example:
Print a list of all matches:
import re
txt = "The rain in Spain"
x = re.findall("ai", txt)
print(x)
The list contains the matches in the order they are found.
If no matches are found, an empty list is returned:
The search() function searches the string for a match, and returns a Match object if there is a match.
If there is more than one match, only the first occurrence of the match will be returned:
Example:
Search for the first white-space character in the string:
import re
txt = "The rain in Spain"
x = re.search("\s", txt)
print("The first white-space character is located in position:", x.start())
None is returned:split() function returns a list where the string has been split at each match:Example-1:
Split at each white-space character:
import re
txt = "The rain in Spain"
x = re.split("\s", txt)
print(x)
You can control the number of occurrences by specifying the maxsplit parameter:
Example-2:
Split the string only at the first occurrence:
import re
txt = "The rain in Spain"
x = re.split("\s", txt, 1)
print(x)
The sub() function replaces the matches with the text of your choice:
Example-1:
Replace every white-space character with the number 9:
import re
txt = "The rain in Spain"
x = re.sub("\s", "9", txt)
print(x)
We can control the number of replacements by specifying the
countparameter:
Example-2:
Replace the first 2 occurrences:
import re
txt = "The rain in Spain"
x = re.sub("\s", "9", txt, 2)
print(x)
None will be returned, instead of the Match Object.Example-1:
Do a search that will return a Match Object:
import re
txt = "The rain in Spain"
x = re.search("ai", txt)
print(x) #this will print an object
The Match object has properties and methods used to retrieve information about the search, and the result:
.span() returns a tuple containing the start-, and end positions of the match..string returns the string passed into the function.group() returns the part of the string where there was a matchExample-1:
Print the position (start- and end-position) of the first match occurrence.
The regular expression looks for any words that starts with an upper case “S”:
import re
txt = "The rain in Spain"
x = re.search(r"\bS\w+", txt)
print(x.span())
Example-2:
Print the string passed into the function:
import re
txt = "The rain in Spain"
x = re.search(r"\bS\w+", txt)
print(x.string)
Example-3:
Print the part of the string where there was a match.
The regular expression looks for any words that starts with an upper case “S”:
import re
txt = "The rain in Spain"
x = re.search(r"\bS\w+", txt)
print(x.group())
Note: If there is no match, the value None will be returned, instead of the Match Object.