How to Solve Python NameError: name ‘csv’ is not defined

by | Programming, Python, Tips

This error occurs when you try to use the csv module without importing it first. You can solve this error by importing the module using the import keyword. For example,

import csv

filename = 'fiel.csv'

with open(filename, 'r') as csvfile:

    csvreader = csv.reader(csvfile)

    for row in csvreader:

        print(row)

This tutorial will go through how to solve the error with code examples.


NameError: name ‘csv’ is not defined

Python raises the NameError when it cannot recognise a name in our program. In other words, the name we are trying to use is not defined in the local or global scope. A name can be related to a built-in function, module, or something we define in our programs, like a variable or a function.

The error typically arises when:

  • We misspell a name
  • We do not define a variable or function
  • We do not import a module

In this tutorial, the source of the error NameError: name ‘csv‘ is not defined is usually due to not importing the module. Let’s look at an example.

Example

The Python csv module implements classes to read and write tabular data in Comma Separated Values (CSV) format. We can use the csv module’s reader and writer objects to read and write sequences respectively. Let’s look at an example of writing some data to a csv file using the writer() method:

rows = [['name', 'mass', 'charge', 'spin'],
['electron', '0.511', '-1', '1/2'],
        ['muon', '105.7', '-1', '1/2'], 
        ['proton','938.3', '+1', '1/2'],
        ['Z-boson','80433', '0', '0']]

filename = 'particles_info.csv'

with open(filename, 'w') as csvf:

    csvwriter = csv.writer(csvf)

    csvwriter.writerows(rows)

In the above code, we define a nested list, where each list is a row of strings. The first list are the fields we want to appear in the csv file and the remaining lists are the rows containing the information for each field.

Then we use a context manager to open a file in write mode, create a writer object using csv.writer() and then csv.writerows() to write the multiple rows.

Let’s run the code to see what happens:

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Input In [1], in <cell line: 9>()
      7 filename = 'particles_info.csv'
      9 with open(filename, 'w') as csvf:
---> 11     csvwriter = csv.writer(csvf)
     12     csvwriter.writerows(rows)

NameError: name 'csv' is not defined

The error occurred because we did not import the csv module. Although csv is a built-in module we still need to import it.

Solution #1: Use import keyword

We can import the module by putting an import statement at the top of the program. Let’s look at the update code:

import csv

rows = [['name', 'mass', 'charge', 'spin'],
        ['electron', '0.511', '-1', '1/2'],
        ['muon', '105.7', '-1', '1/2'], 
        ['proton','938.3', '+1', '1/2'],
        ['Z-boson','80433', '0', '0']]

filename = 'particles_info.csv'

with open(filename, 'w') as csvf:

    csvwriter = csv.writer(csvf)

    csvwriter.writerows(rows)

When we run this code, we will successfully create a file in our working directory called particles_info.csv containing the particle information.

Solution #2: Use from keyword

We can also use the from keyword to import a specific variable, class or function from a module. In this case, we want to import the writer class from the csv module.

Using the from keyword means we do not have to specify the csv module in the rest of the program, we only need the writer class.

Let’s look at the updated code:

from csv import writer

rows = [['name', 'mass', 'charge', 'spin'],
        ['electron', '0.511', '-1', '1/2'],
        ['muon', '105.7', '-1', '1/2'], 
        ['proton','938.3', '+1', '1/2'],
        ['Z-boson','80433', '0', '0']]

filename = 'particles_info.csv'

with open(filename, 'w') as csvf:

    csvwriter = writer(csvf)

    csvwriter.writerows(rows)

When we run this code, we will successfully create a file in our working directory called particles_info.csv containing the particle information.

The from keyword is also useful for importing multiple classes, functions or variables from a module. Let’s look at an example of importing the writer and reader classes from the csv module.

from csv import writer, reader

rows = [['name', 'mass', 'charge', 'spin'],
        ['electron', '0.511', '-1', '1/2'],
        ['muon', '105.7', '-1', '1/2'], 
        ['proton','938.3', '+1', '1/2'],
        ['Z-boson','80433', '0', '0']]

filename = 'particles_info.csv'

with open(filename, 'w') as csvf:

    csvwriter = writer(csvf)

    csvwriter.writerows(rows)

with open(filename, 'r') as csvf:

    csvreader = reader(csvf)

    fields = next(csvreader)

    for row in csvreader:

        print(row)

In the above code, we use the writer() class to create a writer object and write the data to a csv file. Then, we use the reader() class to create a reader object to read the data from the file and print each row as a list of strings.

Let’s run the code to get the result:

['electron', '0.511', '-1', '1/2']
['muon', '105.7', '-1', '1/2']
['proton', '938.3', '+1', '1/2']
['Z-boson', '80433', '0', '0']

Summary

Congratulations on reading to the end of this tutorial!

For further reading on NameErrors, go to the articles:

To learn more about Python for data science and machine learning, go to the online courses page on Python for the most comprehensive courses available.

Have fun and happy researching!

Research Scientist at Moogsoft | + posts

Suf is a research scientist at Moogsoft, specializing in Natural Language Processing and Complex Networks. Previously he was a Postdoctoral Research Fellow in Data Science working on adaptations of cutting-edge physics analysis techniques to data-intensive problems in industry. In another life, he was an experimental particle physicist working on the ATLAS Experiment of the Large Hadron Collider. His passion is to share his experience as an academic moving into industry while continuing to pursue research. Find out more about the creator of the Research Scientist Pod here and sign up to the mailing list here!

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