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 \"\", line 1, in 
 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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