Python Programming

As a reminder, here are the special metacharacters for regular expressions in Python

• .: Match any characters except a newline.
• ^: Match the start of a string, or “not” if used inside [ ].
• $: Match the end of a string
• ?: Match zero or one repetitions
• *: Match zero or more repetitions
• +: Match one or more repretitions
• [ ]: Match a set of characters
• ( ): Grouping
• |: Or
• {m}: Match exactly m repetitions
• {m,n}: Match m to n repetitions. Omitting n will give you infinity.
• \: Escape characters. Use this to represent any of the metacharacters above (e.g. “\?” if you want to match a question mark)

Here are also some special characters that can be used as a shorthand for the corresonding regular expressions:

• \d == [0-9] (“digits”)
• \D == [^0-9] (“non-digits”)
• \s == [ \t\n\r\f\v] (“whitespace”)
• \S == [^ \t\n\r\f\v] (“non-whitespace”)
• \w == [a-zA-Z0-9_] (“word”)
• \W == [^a-zA-Z0-9_] (“non-word”)

Also remember the curse of the backslash \. If you want to represent a single backslash, you will need to escape it with another backslash "\\". For example if you want to represent a newline character \n, it should be written as "\\n". If you want two backslashes \\, then you will need to represent it with four backslashes "\\\\". Alternatively, you can use a Python raw string literal: r"\n" is equivalent to "\\n", and r"\\" is equivalent to "\\\\".