An overview of main functions from the Python re module.

python_re_functions.py

"""
Good reference: https://www.dataquest.io/cheat-sheet/regular-expressions-cheat-sheet/
Official documentation: https://docs.python.org/3/library/re.html
"""

import re 

text = "dog cat dog"

########## re.findall() ##########
"""
Returns a list of strings, the elements of which are each all non-overlapping matches of the pattern:
"""
matches = re.findall("dog", text) # Returns ["dog", "dog"]

########## re.search() ##########
"""
Returns a Match object for the first match of the pattern:
"""
match = re.search("dog", text)
match.group() # This returns the matched string.

########## re.match() ##########
"""
Only returns if a match if the pattern is found at start of the string.
"""
match = re.match("cat", text) # Returns None.
match = re.match("dog", text) # Returns a Match object.

########## re.fullmatch() ##########
"""
Only returns if a match if the pattern matches the entire string.
"""
match = re.fullmatch("dog", text) # This won't return a match despite the pattern matching SOME of the string.
match = re.fullmatch(".*dog", text) # This will match.

########## re.compile() ##########
"""
Compile a regular expression pattern into a Pattern object, which can be used for matching using its match(), 
search() and other methods.
"""
pattern = re.compile("*.cat") # Pattern object.
match = pattern.match(text) 
# the above code is equivelent to:
match = re.match("*.cat", text)

########## re.sub() ##########
"""
Replaces all matches with the specified string.
"""
replacement = re.sub("dog", "fish", text) # Returns "fish cat fish"