Write a simple regex to validate a username. Allowed characters are:

- lowercase letters,
- numbers,
- underscore

Length should be between 4 and 16 characters (both included).

Difficulty: introductory

Starter code:

def validate_usr(username):
	

Solutions:
import re
def validate_usr(un):
    return re.match('^[a-z0-9_]{4,16}$', un) != None

import re

def validate_usr(username):
    return bool(re.match(r'^[a-z0-9_]{4,16}$', username))

import re
validate_usr = lambda str: bool(re.match('^[a-z\d_]{4,16}$', str))

import re
def validate_usr(username):
    return re.match(r"^[a-z0-9_]{4,16}$",username) is not None

def validate_usr(username):
    if len(username) < 4 or len(username) > 16:
        return False 
    allowed = 'abcdefghijklmnopqrstuvwxyz0123456789_'
    for i in username:
        if i not in allowed:
            return False
    return True

def validate_usr(username):
    numeric="0123456789"
    if len(username)>=4 and len(username)<=16:
        for letter in username:
            status = 0
            if letter.islower() or letter == "_":
                status = 1
            for num in numeric:
                if letter == num:
                    status = 1
            if status == 0:
                return False
        return True
    else:
        return False

import re
def validate_usr(username):
    return re.match("^[a-z0-9_]{4,16}$", username) is not None


import re
def validate_usr(username):
    if re.match(r'^[a-z0-9_]{4,16}$', username):
        return True
    else:
        return False


def validate_usr(user):
  return 3 < len(user) < 17 and all(c in 'abcdefghijklmnopqrstuvwxyz_0123456789' for c in user)

from re import fullmatch

def validate_usr(username):
    return bool(fullmatch(r"[_0-9a-z]{4,16}", username))