Regular expressions in Python

#Regular expressions - 

Checking the documentation of re 

import re
help(re)
dir(re)

The re.compile() function returns a regular expression object. This object represents the compiled version of the regular expression pattern.

import re

pattern = re.compile(r'\d+')  # This pattern matches one or more digits.

So, in the regular expression pattern \d{4}, \d is used to match exactly one digit, and {4} specifies that this digit should occur exactly four times in sequence. Therefore, \d{4} is a pattern that matches sequences of four consecutive digits.

string = "The Euro STOXX 600 index, which tracks all stock markets across Europe including the 

FTSE, fell by 11.48% – the worst day since it launched in 1998. The panic selling prompted by 

the coronavirus has wiped £2.7tn off the value of 

STOXX 600 shares since its all-time peak on 19 

February."

import re

# Define a raw string with a regular expression pattern

s = r"\d{4}"

# Compile the regular expression pattern

t = re.compile(s)

# Use the compiled pattern to find all occurrences in the string

result = re.findall(t, string)

# Print the result

print(result)

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>>> import re

>>> result = re.search(r"\d{3}", string)

>>> result

<re.Match object; span=(15, 18), match='600'>

So, in the regular expression pattern \d{4}, \d is used to match exactly one digit, and {4} specifies that this digit should occur exactly four times in sequence. Therefore, \d{4} is a pattern that matches sequences of four consecutive digits.

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Here's a brief breakdown of how the pattern works:

\w: Match a single word character (alphanumeric character or underscore).

{3}: Match exactly three occurrences of the preceding word character

>>> result = re.match(r"\w{3}", string)

>>> result

<re.Match object; span=(0, 3), match='The'>

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>>> result = re.findall(r"\d{3}", string)

>>> result

['600', '199', '600']

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>>> result = re.split(r"\s", string)

>>> result

['The', 'Euro', 'STOXX', '600', 'index,', 'which', 'tracks', 'all', 'stock', 'markets', 'across', 'Europe', 'including', 'the', '', 'FTSE,', 'fell', 'by', '11.48%', '–', 'the', 'worst', 'day', 'since', 'it', 'launched', 'in', '1998.', 'The', 'panic', 'selling', 'prompted', 'by', 'the', 'coronavirus', 'has', 'wiped', '£2.7tn', 'off', 'the', 'value', 'of', 'STOXX', '600', 'shares', 'since', 'its', 'all-time', 'peak', 'on', '19', 'February.']

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>>> result = re.sub(r"[A-Z]{2,}", "INDEX",string)

>>> result

'The Euro INDEX 600 index, which tracks all stock markets across Europe including the  INDEX, fell by 11.48% – the worst day since it launched in 1998. The panic selling prompted by the coronavirus has wiped £2.7tn off the value of INDEX 600 shares since its all-time peak on 19 February.'

In simpler terms, the re.sub() function is replacing any sequence of two or more consecutive uppercase letters in the original string with the word "INDEX".

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>>> result = re.findall(r"the", string)

>>> result

['the', 'the', 'the', 'the']

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'''Prints three charecters of decimals'''

string = "The Euro STOXX 600 index, which tracks all stock markets across Europe including the FTSE, fell by 11.48% – the worst day since it launched in 1998. The panic selling prompted by the coronavirus has wiped £2.7tn off the value of STOXX 600 shares since its all-time peak on 19 February."

import re

result = re.findall(r"\d{3}", string)

print(result)

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'''Spilts all words into List of charecters '''

string = "The Euro STOXX 600 index, which tracks all stock markets across Europe including the FTSE, fell by 11.48% – the worst day since it launched in 1998. The panic selling prompted by the coronavirus has wiped £2.7tn off the value of STOXX 600 shares since its all-time peak on 19 February."

import re

result = re.split(r"\s", string)

print(result)

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'''It will remove the Index charecter'''

import re

pattern = r'\d+'  # This is a regular expression pattern to match one or more digits

replacement = 'X'

text = 'There are 123 apples and 456 oranges.'

result = re.sub(pattern, replacement, text)

print(result)

'''Output -- There are X apples and X oranges.'''

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