Printing alternate lines using python

for i, line in enumerate(file('myfile.txt')):

   if i % 5 in (0, 1):
       print line

f = open('filename.txt', 'r')
for index, line in enumerate(f.readlines()):
    if index%5 <= 1:
       print(line)

Regular expressions

Username:
/^[a-z0-9_-]{3,16}$/

 Password:
/^[a-z0-9_-]{6,18}$/

 Matchign an email:
/^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/

 Matching a phone numeber:
^(\+\d{1,2}\s)?\(?\d{3}\)?[\s.-]\d{3}[\s.-]\d{4}$
123-456-7890
(123) 456-7890
123 456 7890
123.456.7890
+91 (123) 456-7890

 IP address
/^(?:(?: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]?)$/

print specific lines from files

searchquery = 'am'

with open('Test.txt') as f1:
    with open('Output.txt', 'a') as f2:
        lines = f1.readlines()
        for i, line in enumerate(lines):
            if line.startswith(searchquery):
                f2.write(line)
                f2.write(lines[i + 1])
                f2.write(lines[i + 2]