REGULAR EXPRESSION IN PYTHON

Regular expressions are used to extract the required information from the given data by following patterns. Regular expressions are also used to check whether the given input data is in proper format or not. Example – Email-Id verification, Mobile number verification, Password validation and so on. The regular expressions which are supported by Perl are also supported by python. Python is providing the built-in functions to work with the regular expression easily. All the predefined functions which are related to regular expression are present in re module.

Special characters which are used in regular expression are –

• ·       * ----> It matches zero or more occurrences of preceding character.

          Example –

          ab*c

          ac

          abc

          abbc

          abbbbbbc

          bbdc #Error

• ·       + ----> It matches one or more occurrences of preceding character.

          Example –

          ab+c

          ac #Error

          abc

          abbc

          abbbbc

• ·       ? ----> It matches zero or one occurrence of preceding character.

          Example –

          ab?c

          ac

          abc

          abbc #Error

• ·       . ----> It matches any single character.

Example –

a.c

agc

asc

a$c

abcd #Error

• ·       [ ] ----> It matches any single character to given list.

Example –

b[aeiou]d

bad

bed

bid

bod

bud

bgd #Error

• ·       [^] ----> It matches any single character other than in the given list.

Example –

b[^aeiou]d

bad #Error

bed #Error

bid #Error

bod #Error

bud #Error

bgd

• ·       [-] ----> It matches any single character in the given range.

Example –

x[a-e]y

xay

xby

xey

xfy #Error

[0-9] ---->any single digit.

[a-z] ----> any one lowercase alphabet

[A-Z] ----> any one uppercase alphabet

[a-zA-Z] ----> any one alphabet

[a-zA-Z0-9] ----> any one alphanumeric

[^0-9] ----> any single non-digit

[^A-Z] ----> any one non uppercase alphabet

[^a-z] ----> any one non lowercase alphabet

[^a-zA-Z] ----> any one non-alphabet

[^a-zA-Z0-9] ----> any one non-alphanumeric

• ·       (|) ----> Match anyone string in the list.

Example –

(java|hadoop|python)

java

hadoop

python

php #Error

• ·       {m} ----> It matches exact occurrence of preceding character.

Example –

ab{3}c

abc #Error

abbc #Error

abbbc

• ·  {m,n} ----> It matches minimum m occurrence and maximum n occurrence of preceding character.

Example –

ab{3,5}c

abbc #Error

abbbc

abbbbc

• ·  {m,} ----> It matches minimum m occurrence and maximum no limit of preceding character.

Example –

ab{3,}c

abc

abbbbbbbc

• ·       ^ ----> Start of the line

Example –

^Python

• ·       $ ----> End of the line

Example –

Python$

• ·       \d or [0-9] ----> any single digit

Example –

[0-9][0-9][0-9] or [0-9]{3} or \d\d\d or \d{3}

• ·       \D or [^0-9] ---->any single non-digit
• ·       \w or [a-zA-Z0-9] ----> any alphanumeric
• ·       \W or [^a-zA-Z0-9] ----> any non alphanumeric (special characters)
• ·       \s ----> “, ‘, \t, \n
• ·       \b ----> word boundary