Python notes(2)

Regular expression

Can be accessed by re module. Basic syntax example:

import re

pattern = r"pam"

match = re.search(pattern, "eggspamsausage")
if match:
    print(match.group())
    print(match.start())
    print(match.end())
    print(match.span())

Here r means “raw string”. group() gives the match string. Output:

>>>
pam
4
7
(4, 7)
>>>

Search and Replace

Syntax: re.sub(pattern, repl, string, max=0) Example:

import re

str = "My name is David. Hi David."
pattern = r"David"
newstr = re.sub(pattern, "Amy", str)
print(newstr)

Mini Cheatsheet

• . any character
• ^ start of string
• $ end of string
• [abc] any one character of ‘a’, ‘b’, or ‘c’
• [A-Za-z] any one letter of any case
• [^A-Z] not upper class letters
• * zero or more repetitions of the previous thing
• + one or more repetitions of the previous thing
• ? zero or one of the previous thing
• {x,y} between ‘x’ and ‘y’ repetitions. default x=0, y=infinity
• (abc) “abc” as a group, taken as a whole when checking for repetitions
• | or
• \2 match two times
• \d \s \w digits, whitespace, word characters
• \D \S \W opposite to above