Let us see how to extract IP addresses from a file using Python.
 

Algorithm :  

• Import the re module forregular expression.
• Open the file using the open() function.
• Read all the lines in the file and store them in a list.
• Declare the pattern for IP addresses. The regex pattern is : 
   

r'(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})'

• For every element of the list search for the pattern using the search() function, store the IP addresses in a list.
• Display the list containing the IP addresses.

The file to be processed is test.txt : 
 

# importing the moduleimportre# opening and reading the filewithopen('C:/Users/user/Desktop/New Text Document.txt')asfh:fstring=fh.readlines()# declaring the regex pattern for IP addressespattern=re.compile(r'(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})')# initializing the list objectlst=[]# extracting the IP addressesforlineinfstring:lst.append(pattern.search(line)[0])# displaying the extracted IP addressesprint(lst)

Output :

The above Python program displays any kind of IP addresses present in the file. We can also display thevalid IP addresses.

Rules for a valid IP Address : 

• The numbers should be in a range of 0-255
• It should consist of 4 cells separated by '.'

The regular expression for valid IP addresses is :
 

((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)

Explanation of Regular Expression used for valid IP:

Since we cannot use 0-255 range in regular expression we divide the same in 3 groups:

• 25[0-5] - represents numbers from 250 to 255
• 2[0-4][0-9] - represents numbers from 200 to 249
• [01]?[0-9][0-9]?- represents numbers from 0 to 199

The file to be processed is test2.txt : 
 

# importing the moduleimportre# opening and reading the filewithopen('test2.txt')asfh:string=fh.readlines()# declaring the regex pattern for IP addressespattern=re.compile('''((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)''')# initializing the list objectsvalid=[]invalid=[]# extracting the IP addressesforlineinstring:line=line.rstrip()result=pattern.search(line)# valid IP addressesifresult:valid.append(line)# invalid IP addresseselse:invalid.append(line)# displaying the IP addressesprint("Valid IPs")print(valid)print("Invalid IPs")print(invalid)

Output :