Check whether a variable is defined or not in Python

The topic deals with the Python variables. Here we are going to determine if a Python variable exists or not.

Certainly, a variable is a container of data. In other words, we can store our data in a variable that we can use for our task.

Defining a Variable :

Data or information needs to be stored for future operations. Moreover, Variable gives the facility to store data.

Let’s see how we define a variable in Python.

a = 4           # a is the variable which stores some data

b = 12.9

c = "Hello"     # Defining a variable

print (a,b,c)   # printing the values of the variable

Output :

4 12.9 Hello

Now let’s continue to our topic without wasting any more time…

Check if a variable is defined or not in Python :

A very simple method to check,

Certainly, this is the topic to be dealt with. So let’s see below:

• First of all, if a variable is defined, it would have some data in it.
• If it is not defined then no data is there in it.

The following example will clear the concept regarding this,

a = 4           # a is the variable which stores some data

b = 12.9

c = "Hello"     # Defining a variable


print (c)       # c is defined so no error is raised

print (d)       # d is not defined so error is raised

Output :

Hello
Traceback (most recent call last):
File "main.py", line 10, in <module>
print (d)
NameError: name 'd' is not defined

So we can see, that there will be an error appear if our variable is not defined.

We can check the existence of a variable using the Python try and except can be used to deal with the following conditions.

• The code is written in the try block.
• If any kind of error arises, then statements in except block get executed.
• If there is no error, except block statements, they are not executed.

The following example may clarify the doubts regarding the use of try/except if any,

a = 10    # a is defined

try:
    print (c)     # variable c is not defined.
                  # therefore error raises and control shifts to except block.

except:
    print ("Variable is not defined") 

Output :

Variable is not defined

Also,read:

• Variable as Dictionary key in Python

This is the way to determine or check whether a variable is defined or not in Python.

One response to “Check whether a variable is defined or not in Python”

1. beta-tester says:

   December 1, 2022 at 2:52 am

   a “try: .. except: ” block is pretty expensiv for just checking if a variable is defined, specially if it is checked like this in a loop.

   normally you can check it with:
   “`python
   if ‘c’ in dir():
   print (c)
   else:
   print (“Variable is not defined”)
   “`
   to check if a variable is in a class dir() or dir().

   Reply