NameError: name 'plt' is not defined in Python [Solved]

# NameError: name 'plt' is not defined in Python

The Python "NameError: name 'plt' is not defined" occurs when we use the pyplot module without importing it first.

To solve the error, install matplotlib and import plt (import matplotlib.pyplot as plt) before using it.

Open your terminal in your project's root directory and install the matplotlib module.

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# 👇️ In a virtual environment or using Python 2
pip install matplotlib

# 👇️ For python 3 (could also be pip3.10 depending on your version)
pip3 install matplotlib

If you get a permissions error on macOS or Linux, use the sudo prefix.

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# 👇️ If you get a permissions error
sudo pip3 install matplotlib

If you don't have pip in your PATH environment variable, use the python -m pip command.

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# 👇️ If you don't have pip in your PATH environment variable
python -m pip install matplotlib

# 👇️ For python 3 (could also be pip3.10 depending on your version)
python3 -m pip install matplotlib

# 👇️ Alternative for Ubuntu/Debian
sudo apt-get install python3-matplotlib

# 👇️ alternative for CentOS
sudo yum install python3-matplotlib

# 👇️ alternative for Fedora
sudo yum install python3-matplotlib

# 👇️ For Anaconda
conda install -c conda-forge matplotlib

# 👇️ For Jupyter Notebook
!pip install matplotlib

After you install the matplotlib module, make sure to import pyplot before using it.

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# 👇️ import pyplot and alias it as plt
import matplotlib.pyplot as plt

fig, ax = plt.subplots()

print(fig)
print(ax)

We used an alias to import the pyplot module from matplotlib as plt.

We imported matplotlib.pyplot and aliased it to plt, so you would access any pyplot methods as plt.plot(), plt.ylabel(), plt.show(), etc.

Make sure you haven't misspelled the module you are importing because module names are case-sensitive.

You can also use from in your import statement when importing pyplot and aliasing it.

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from matplotlib import pyplot as plt

fig, ax = plt.subplots()

print(fig)
print(ax)

The two code samples achieve the same result. They import pyplot from matplotlib and alias it to plt.

# Make sure to not import the matplotlib module in a nested scope

Make sure you haven't placed your import statement in a nested scope, e.g. a function.

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def example():
    import matplotlib.pyplot as plt

    fig, ax = plt.subplots()

    print(fig)
    print(ax)


# ⛔️ NameError: name 'plt' is not defined
fig, ax = plt.subplots()

We imported the matplotlib module in a function, so we aren't able to use it outside of the function.

Import the module at the top level to be able to use it throughout your code.

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# ✅ Moved import to top level
import matplotlib.pyplot as plt


def example():

    fig, ax = plt.subplots()

    print(fig)
    print(ax)


fig, ax = plt.subplots()

print(fig)
print(ax)

The import statement for the matplotlib module has to come at the top of the file before any code that makes use of it.

# Make sure to not import the matplotlib module in a try/except statement

You also should be importing the matplotlib module in a try/except statement.

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try:
    # 👉️ Code here could raise an error

    import matplotlib.pyplot as plt
    fig, ax = plt.subplots()

    print(fig)
    print(ax)
except ImportError:
    fig, ax = plt.subplots()


fig, ax = plt.subplots()

The code sample works, however, if the code in the try statement raises an error, the matplotlib module won't get imported successfully.

This would cause the error because we are trying to access properties on the matplotlib module in the outer scope and the except block.

Instead, move the import statement to the top of the file.

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# ✅ Moved import to the top of the file
import matplotlib.pyplot as plt

try:
    fig, ax = plt.subplots()

    print(fig)
    print(ax)
except ImportError:
    fig, ax = plt.subplots()


fig, ax = plt.subplots()

# NameError: name 'matplotlib' is not defined in Python

The solution to the "NameError: name 'matplotlib' is not defined" is the same.

After you install the matplotlib module, you have to import it before you are able to use it in your code.

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# ✅ Import matplotlib.pyplot and alias it to plt
import matplotlib.pyplot as plt

# ✅ Import matplotlib.image and alias it to pmimg
import matplotlib.image as mpimg


fig, ax = plt.subplots()

print(fig)
print(ax)

img = mpimg.imread('../../doc/_static/stinkbug.png')
print(img)

We used aliases when importing from matplotlib.

We imported matplotlib.pyplot and aliased it to plt, so you would access any pyplot methods as plt.plot(), plt.ylabel(), plt.show(), etc.

Make sure you haven't misspelled the module you are importing because module names are case-sensitive.

Also, make sure you haven't imported from matplotlib in a nested scope, e.g. a function. Import the module at the top level to be able to use it throughout your code.

If you get the error ModuleNotFoundError: No module named 'matplotlib', click on the link and follow the instructions.