What is the difference between re.search and re.match?

 

re.match is anchored at the beginning of the string. That has nothing to do with newlines, so it is not the same as using ^ in the pattern.

As the re.match documentation says:

If zero or more characters at the beginning of string match the regular expression pattern, return a corresponding MatchObject instance. Return None if the string does not match the pattern; note that this is different from a zero-length match.

Note: If you want to locate a match anywhere in string, use search() instead.

re.search searches the entire string, as the documentation says:

Scan through string looking for a location where the regular expression pattern produces a match, and return a corresponding MatchObject instance. Return None if no position in the string matches the pattern; note that this is different from finding a zero-length match at some point in the string.

So if you need to match at the beginning of the string, or to match the entire string use match. It is faster. Otherwise use search.

The documentation has a specific section for match vs. search that also covers multiline strings:

Python offers two different primitive operations based on regular expressions: match checks for a match only at the beginning of the string, while search checks for a match anywhere in the string (this is what Perl does by default).

Note that match may differ from search even when using a regular expression beginning with '^': '^' matches only at the start of the string, or in MULTILINE mode also immediately following a newline. The “match” operation succeeds only if the pattern matches at the start of the string regardless of mode, or at the starting position given by the optional pos argument regardless of whether a newline precedes it.

Now, enough talk. Time to see some example code:

# example code:
string_with_newlines = """something
someotherthing"""

import re

print re.match('some', string_with_newlines) # matches
print re.match('someother', 
               string_with_newlines) # won't match
print re.match('^someother', string_with_newlines, 
               re.MULTILINE) # also won't match
print re.search('someother', 
                string_with_newlines) # finds something
print re.search('^someother', string_with_newlines, 
                re.MULTILINE) # also finds something

m = re.compile('thing$', re.MULTILINE)

print m.match(string_with_newlines) # no match
print m.match(string_with_newlines, pos=4) # matches
print m.search(string_with_newlines, 
               re.MULTILINE) # also matches


Python | re.search() vs re.match()

Prerequisite: Regex in Python
Use of re.search() and re.match() – 
re.search() and re.match() both are functions of re module in python. These functions are very efficient and fast for searching in strings. The function searches for some substring in a string and returns a match object if found, else it returns none.
re.search() vs re.match() – 
There is a difference between the use of both functions. Both return the first match of a substring found in the string,

but re.match() searches only from the beginning of the string and return match object if found. But if a match of substring is found somewhere in the middle of the string, it returns none. 
While re.search() searches for the whole string even if the string contains multi-lines and tries to find a match of the substring in all the lines of string.

# import re module
import re
 
Substring ='string'
 
 
String1 ='''We are learning regex with geeksforgeeks 
         regex is very useful for string matching.
          It is fast too.'''
String2 ='''string We are learning regex with geeksforgeeks 
         regex is very useful for string matching.
          It is fast too.'''
 
# Use of re.search() Method
print(re.search(Substring, String1, re.IGNORECASE))
# Use of re.match() Method
print(re.match(Substring, String1, re.IGNORECASE))
 
# Use of re.search() Method
print(re.search(Substring, String2, re.IGNORECASE))
# Use of re.match() Method
print(re.match(Substring, String2, re.IGNORECASE))

 

Conclusion : 
 

    1. re.search() is returning match object and implies that first match found at index 69.
    2. re.match() is returning none because match exists in the second line of the string and re.match() only works if the match is found at the beginning of the string. 
       
    3. re.IGNORECASE is used to ignore the case sensitivity in the strings. 
       
    4. Both re.search() and re.match() returns only the first occurrence of a substring in the string and ignore others.