Some Advanced usage on regex

get float number:

import re
target = 'total growth is : 8%-8.5%'
rate = re.findall('(\d+(?:\.\d+)?)', target)
print(rate)
['8', '8.5']
#\d is any int, + is one to many
#(?:...)
#A non-capturing group allows you to apply quantifiers to part of your regex but does not capture/assign an ID.
#so it means: find int or, if int follows a "." and any int afterwards, combine the int with ".int"
#For example, repeating 1-3 digits and a period 3 times can be done like #this: /(?:\d{1,3}\.){3}\d{1,3}/
#above regex can match string like : 219.254.232.123 or 232.212.222.3434 (can only go until 232.212.222.343), 
#can not match 232.2122.222.3434 or 232.212.22a.3434

#`(\d+(?:\.\d+)?)` is a group, so result will be put in a list. 

#if you just want to match any int or .xxx or xxxx.xxx,just use

rate = re.findall('(\d+(\.\d+)?)', target)
print(rate)
[('8', ''), ('8.5', '.5')]
#which will return a list to you

#if you just want to find a float, use below: 

target = 'total growth is : 8%-8.5% or 9.546%'
rate = re.findall('(\d+\.\d+)', target)
print(rate)
['8.5', '9.546']

A bit deeper:

A(?=B) ：Match String A ends with String B
A(?!B) ：Match String A NOT end with String B
(?<=B)A ：Match String A start with String B
(?<!B)A ： Match String A NOT start with String B

target = 'in 2021 financial year total growth is : 8%-8.5% or 9.546%'

rate = re.findall(r'(\d+(?:\.\d+)?)(?![\d financial])', target)

print(rate)
['8', '8.5', '9.546']

# :! means **NOT end** with 
# ?![\d financial] means number followed by " financial" or a digit, so 2021 is totally excluded. if with only ?![ financial], it wil match 202

Find any number before %

target = 'in 2021 financial year total growth is : 8%-8.5% or 9.546%'
rate = re.findall('\d+(?=%)', target)
print(rate)
['8', '5', '546']

#to find float before % : 
rate = re.findall('(\d+\.\d+)(?=%)', target) #combine previous regex
print(rate)
['8.5', '9.546']

# to find int or float before %: 
rate = re.findall('(\d+(?:\.\d+)?)(?=%)', target)  #combine previous regex
print(rate)
['8', '8.5', '9.546']

# find year: 

rate = re.findall('\d+(?= financial)', target)
print(rate)
['2021']

No. 2 test:

A(?!B) ：Match String A NOT end with String B

# find any number not end with " financial"
rate = re.findall('\d+(?![\d financial])', target)
print(rate)
['8', '8', '5', '9', '546']

No. 3 test:

(?<=B)A ：Match String A start with String B

text = 'Price: $10000.00'
print(re.findall(r'(?<=\$)\d+', text))
['10000']

No. 4 test:

(?<!B)A ： Match String A NOT start with String B

text = 'Price: $10000.00, Quantity: 5'
print(re.findall(r'(?<![\d\$\.])\d+', text))  
['5']

Now come to the import ant one, regex for a IPv4 address

IPPattern = re.compile('(?<![\.\d])(?:25[0-5]\.|2[0-4]\d\.|[1]\d\d\.|[1-9]\d\.|[1-9]\.)(?:25[0-5]\.|2[0-4]\d\.|[01]?\d\d?\.){2}(?:25[0-5]|2[0-4]\d|[01]?\d\d?)(?![\.\d])')

IPv4 Regex test result