s18.py

#identifier should not contain empty spaces
s1="Hello 123"
print (s1.isidentifier())#Output:False

#Identifier should not begin with numbers
s2="123hello"
print (s2.isidentifier())#Output:False


s3="_hello"
print (s3.isidentifier())#Output:True


s4="hello_123"
print (s4.isidentifier())#Output:True


#empty string
s5=""
print (s5.isidentifier())#Output:False


#white spaces
s6=" "
print (s6.isidentifier())#Output:False


#special characters are not allowed in identifiers
s7="hello@#$"
print (s7.isidentifier())#Output:False