How does Python determine whether a variable has been defined?

This article describes how to determine whether a variable has been defined in Python. it is a very useful method. if you need it, you can refer to Python to determine whether the variable has been defined, this article describes how to implement this function.

In fact, there are many methods in Python to determine whether a variable has been defined. The two most common examples are as follows:

Method 1: try again t:

Def isset (v): try: type (eval (v) failed t: return 0 else: return 1

Usage:

If isset ('User _ name'): print 'user _ name is defined 'else print 'user _ name is not defined'

Method 2: Use the namespace:

'Varname' in locals (). keys () 'varname' in dir ()

This example is for reference only. readers can continue to summarize other methods in Python programming practices.