Python如何實(shí)現(xiàn)判斷字符串是否為合法的標(biāo)示符

# python2.x
import keyword
print keyword.kwlis
# python3.x
import keyword
print(keyword.kwlist)


# python2.x輸出：
 ['and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'exec', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'not', 'or', 'pass', 'print', 'raise', 'return', 'try', 'while', 'with', 'yield']
# 共31個(gè)
# python3.x輸出：
['False', 'None', 'True', 'and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
# 共33個(gè)

# python2.7

#!/usr/bin/env python
# -*- coding: UTF-8 -*-
import keyword
import string
def is_signal(s):
 kw = keyword.kwlist
 if s in kw:
  return 0
 elif s[0] == '_' or s[0] in string.letters: # 判斷是否為字母或下劃線開(kāi)頭
  for i in s:
   if i == '_' or i in string.letters or i in string.digits: # 判斷是否由字母數(shù)字或下劃線組成
    pass
   else:
    return 0
  return 1
 else:
  return 0
def main():
 s = raw_input()
 if is_signal(s) == 1:
  print "True"
 else:
  print "False"
if __name__ == '__main__':
 main()

# python3.4

#!/usr/bin/env python
# -*- coding: UTF-8 -*-
import keyword
import string
def is_signal(s):
 kw = keyword.kwlist
 if s in kw:
  return 0
 elif s[0] == '_' or s[0] in string.ascii_letters: # 判斷是否為字母或下劃線開(kāi)頭
  for i in s:
   if i == '_' or i in string.ascii_letters or i in string.digits: # 判斷是否由字母數(shù)字或下劃線組成
    pass
   else:
    return 0
  return 1
 else:
  return 0
def main():
 s = input()
 if is_signal(s) == 1:
  print("True")
 else:
  print("False")
if __name__ == '__main__':
 main()

#!/usr/bin/env python
'''
idcheck.py -- checks identifiers for validity
'''
 
import string    # string utility module
 
# create alphabet and number sets
alphas = string.ascii_letters + '_'
nums = string.digits
 
# salutation message and input prompt
print ('Welcome to the Identifier Checker v1.0')
print ('Testees must be at least 2 chars long.')
inp = input('Identifier to test ?')
 
if len(inp) >= 1:
 
  if inp[0] not in alphas:
    print ('invalid: first symbol must be alphabetic')
 
  else:
    for otherChar in inp[1:]:
      if otherChar not in alphas + nums:
        print ('invalid: remaining symbols must be alphanumeric')
        break
    else:
      print ("okay as an identifier")
else:
  print ('invalid: length must be >= 1')

Welcome to the Identifier Checker v1.0
Testees must be at least 2 chars long.
Identifier to test -> 123_das
invalid: first symbol must be alphabetic

Welcome to the Identifier Checker v1.0
Testees must be at least 2 chars long.
Identifier to test -> _123sdad
okay as an identifier