Check if a Column Exists in a Pandas DataFrame

In this tutorial, we will learn to check if a column exists in a Pandas DataFrame. A good level of exposure to Python is recommended but not required.

How to check if a column exists in a dataframe?

The Pandas dataframe has a built-in method that returns its columns. Using this method, we can obtain the list of columns. We can then check if a column exists in the dataframe. The syntax will be-

column_exists = column in df.columns

Here,

• df — A Pandas DataFrame object.
• df.columns — Dataframe’s attribute that returns a list of columns as a Pandas Series object.

The in operator in Python is used to check if an item exists in the iterable over which it is applied. If the item exists, it returns True; otherwise, it returns False. Here, we have used the in operator to check if the column exists in the Series object returned by the df.columns attribute. Note that Series objects are iterable.

Another method to check if the column exists in the dataframe will be to try accessing the column. If the column exists, we can access the column; otherwise, an error will be raised. This error can be captured safely using a try-except block. The syntax for the same is-

try:
    try_accessing = df[column]
    print(f"Column {column} exists in dataframe df")
except KeyError:
    print(f"Column {column} doesn't exist in dataframe df")

Here, the variables have the same meaning as in the previous code block. Under the try statement, we check if the column can be accessed. If it can’t be accessed, i.e., if the column doesn’t exist in dataframe df, KeyError is raised which is handled using except statement.

Examples

Let’s understand the above code with some examples. To begin, we create a dataframe for the marks of students in a class. For simplicity, we will consider only three students and three subjects.

import pandas as pd

#Making a dictionary to pass it to dataframe
d = {'Mary': [47, 25, 36], 'Alfred': [81, 85, 76], 'Jean': [93, 87, 71]}

#DataFrame object is created with index of choice.
df = pd.DataFrame(d, index=['Maths', 'English', 'Science'])

#Display the dataframe
print(df)

Output:

         Mary  Alfred  Jean
Maths      47      81    93
English    25      85    87
Science    36      76    71

We have the dataframe with subjects as row labels and student names as columns.

Example 1: Check if the column exists using the in operator

To check if the column exists in the given dataframe, we print the result when the in operator is applied to the column and df.columns.

column = 'Mary'
column_exists = column in df.columns
print(column_exists)

Output:

True

The output is True since the column exists in the dataframe. If the column didn’t exist in the dataframe, the output would have been False.

Example 2: Check if the column exists using try-except blocks

In this example, we will try to access the column of a dataframe under the try block. If it raises a KeyError while doing so, then the column doesn’t exist. Or else it exists. The code will be-

column = 'Joseph'
try:
    try_accessing = df[column]
    print(f"Column {column!r} exists in dataframe df")
except KeyError:
    print(f"Column {column!r} doesn't exist in dataframe df")

Output:

Column 'Joseph' doesn't exist in dataframe df

Since the column ‘Joseph’ doesn’t exist, accessing the column in the try block raises a KeyError, and the code under the except block is executed. Note that !r is used only for formatting the output.

Summary

From this tutorial, we looked at how to:

• Use the in operator and the columns method of Pandas DataFrame to check if the column exists in the dataframe.
• Use try-except blocks to check if the column exists in the dataframe.

You might also be interested in –

• Pandas – Check if a column is all one value
• Pandas – Check if Column contains String from List
• Pandas – Check if a DataFrame is Empty
• Pandas – Find Column Names that Start with Specific String
• Pandas – Get Columns with Missing Values