Q:

LDAP search with username as variable

I am using the Python-LDAP module and trying to make a query on the logged in user.  The username will be passed into the query.  When I simply type the username in as a string my results come out correctly.  
But if I try to pass the (username) variable it returns 
LDAPError - FILTER_ERROR: {'desc': u'Bad search filter'}  I've tried a number of different combinations but continue to get the same error returned.  Any insight here would be great!
Edited for Minimal, Complete, and Verifiable example:
import ldap

LDAP_SERVER = "ldap://myldapserver.domain.ad:389"
username = r"domain\serviceAccount"
password = "Password"

l = ldap.initialize(LDAP_SERVER)
def login(username, password):
    try:
        l.simple_bind_s(username, password)
        base = "OU=Users,OU=Group,DC=domain,DC=ad"

        criteria = "(&(objectClass=user)(sAMAccountName=anActualUsername))" #WORKS    
        criteria = '(&(objectClass=user)(sAMAccountName=%s))' % username #DOESNT WORK
        criteria = "(&(objectClass=user)" + "(sAMAccountName=" + username + "))" #DOESNT WORK

        attributes = ['displayName']
        result = l.search_s(base, ldap.SCOPE_SUBTREE, criteria, attributes)
        print result
    except ldap.INVALID_CREDENTIALS:
        return False
    return True

login(username,password)

A:

I needed to use ldap.filter.filter_format for proper character escaping.
import ldap.filter

criteria= ldap.filter.filter_format('(&(objectClass=user)(sAMAccountName=%s))', [username])

