Which is not a legal identifier in python

Identifier is a set of valid strings allowed as names in computer languages.

Pyhon identifier rules:

1. The first character must be a letter or an underscore (_), that is, it cannot Open with numbers.

2. The remaining characters can be letters, numbers and underscores, that is, they cannot contain symbols other than underscores (spaces, operators...).

3. Case sensitive.

4. Python’s reserved keywords cannot be used as identifiers.

5. It is not recommended to use Python's built-in name collection as an identifier.

Python provides the keyword module to query the keyword set and determine whether a string is a python keyword:

Python’s legal identifier

The following code allows the user to input a string and then determine whether it is a legal python identifier. If not, continue inputting until the input is correct and the program exits.

import keyword
import string
def is_valid_py_name(py_name):
    py_name = py_name.strip()
    if keyword.iskeyword(py_name):
        print "'{0}' is a python keyword!".format(py_name)
        return False
    elif py_name == "":
        print "empty input!"
        return False
    elif py_name[0] not in (string.letters+'_'):
        print "'{0}' not start with _ or letter!".format(py_name)
        return False
    else:
        for i in range(1,len(py_name)):
            if py_name[i] not in (string.letters+'_'+string.digits):
                print "'{0}' is invalid letter!".format(py_name[i])
                return False
        print "'{0}' is valid py name!".format(py_name)
        return True
    
if __name__ == "__main__":
    is_valid = False
    while not is_valid:
        print "Please enter a string:"
        py_name = raw_input()
        is_valid = is_valid_py_name(py_name)

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