python变量不能以数字打头详解

在编写python函数时，无意中发现一个问题：python中的变量不能以数字打头，以下函数中定义了一个变量3_num_varchar，执行时报错。

函数如下：

    def database_feild_varchar_trans(in_feild):
      '''
      transfer the feild if varchar then 3times lang else no transfer
      '''
      feild_split = in_feild.split(' ')
      is_varchar = feild_split[1].find('VARCHAR')
      if is_varchar >= 0 :
        num_varchar = feild_split[1].replace('VARCHAR','').replace('(','').replace(')','') 
        print (num_varchar)
        3_num_varchar = num_varchar*3
        feild_split[1] = feild_split[1].replace(str(num_varchar),str(3_num_varchar))
        return feild_split
      else:
        print ('The feild type is not varchar')
        return feild_split

报错信息如下：

    >>> runfile('E:/procedure/python/projects/others/table_test.py', wdir='E:/procedure/python/projects/others')
    Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
     File "D:\Python33\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 699, in runfile
      execfile(filename, namespace)
     File "D:\Python33\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 88, in execfile
      exec(compile(open(filename, 'rb').read(), filename, 'exec'), namespace)
     File "E:/procedure/python/projects/others/table_test.py", line 20
      3_num_varchar = int(num_varchar)*3
            ^
    SyntaxError: invalid syntax

    将变量3_num_varchar改为num_varchar_3，运行成功，程序改为如下：

    import os
    import sys
    str1='aaa varchar(10)'

    def database_feild_varchar_trans(in_feild):
      '''
      transfer the feild if varchar then 3times lang else no transfer
      '''
      feild_split = in_feild.split(' ')
      is_varchar = feild_split[1].find('VARCHAR')
      if is_varchar >= 0 :
        num_varchar = feild_split[1].replace('VARCHAR','').replace('(','').replace(')','') 
        print (num_varchar)
        num_varchar_3 = num_varchar*3
        feild_split[1] = feild_split[1].replace(str(num_varchar),str(num_varchar_3))
        return feild_split
      else:
        print ('The feild type is not varchar')
        return feild_split

    print (database_feild_varchar_trans(str1))

运行结果：

    >>> runfile('E:/procedure/python/projects/others/table_test.py', wdir='E:/procedure/python/projects/others')
    The feild type is not varchar
    ['aaa', 'varchar(10)']

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