NameError: name ‘X’ is not defined in Python

The Python “NameError: name ‘plot_cases_simple’ is not defined” error occurs when you try to access a variable, function, or class that has not been defined or has not yet been declared. This error can occur for a variety of reasons. Here are some common causes and solutions:

Misspelling the Name of an Object

Python is case-sensitive, so make sure to spell the name of the object correctly. For example:

# Incorrect: "plot_cases_simple" is misspelled as "plot_cases_simpl"
def plot_cases_simple(df):
    ax = df.plot(x="Date", y=["Deaths", "Recovered"])
    ax.set_ylabel("Number of cases")
    ax.set_xlabel("Date")
plot_cases_simpl(df)

To fix the error, spell the name of the object correctly:

# Correct: spelling of "plot_cases_simple" is correct
def plot_cases_simple(df):
    ax = df.plot(x="Date", y=["Deaths", "Recovered"])
    ax.set_ylabel("Number of cases")
    ax.set_xlabel("Date")
plot_cases_simple(df)

Accessing an Object Before It Has Been Defined

If you try to access an object before it has been defined, you will get a “NameError: name ‘object_name’ is not defined” error. For example:

# Incorrect: trying to access an object before it has been defined
def plot_cases_simple(df):
    ax = df.plot(x="Date", y=["Deaths", "Recovered"])
    ax.set_ylabel("Number of cases")
    ax.set_xlabel("Date")
    
# This line should come after the definition of plot_cases_simple
plot_cases_simple(df)

To fix the error, make sure to define the object before accessing it:

# Correct: defining plot_cases_simple before calling it
def plot_cases_simple(df):
    ax = df.plot(x="Date", y=["Deaths", "Recovered"])
    ax.set_ylabel("Number of cases")
    ax.set_xlabel("Date")
    
plot_cases_simple(df)

Forgetting to Import a Built-in Module

If you try to use a built-in module without importing it first, you will get a “NameError: name ‘module_name’ is not defined” error. For example:

# Incorrect: trying to access math.floor without importing the math module
print(math.floor(15.5))

# Correct: importing the math module before accessing math.floor
import math
print(math.floor(15.5))

Not Wrapping a String in Quotes

If you forget to wrap a string in quotes, you will get a “NameError: name ‘string’ is not defined” error. For example:

def greet(name):
    return 'Hello ' + name

# Incorrect: forgot to wrap string in quotes
greet(Alice)

# Correct: wrapping string in quotes
greet('Alice')

Not Wrapping a Key of a Dictionary in Quotes

If you forget to wrap a key of a dictionary in quotes, you will get a “NameError: name ‘key’ is not defined” error. For example:

# Incorrect: forgot to wrap key in quotes
employee = {
    'name': 'Alice',
    age: 30  # "age" should be wrapped in quotes
}

# Correct: wrapping key in quotes
employee = {
    'name': 'Alice',
    'age': 30
}

Using a Scoped Variable Outside Its Scope

If you try to access a scoped variable (i.e., a variable defined within a function) outside its scope, you will get a “NameError: name ‘variable_name’ is not defined” error. For example:

def greet(name):
    message = "Hello " + name
    return message

# Incorrect: trying to access a scoped variable outside its scope
print(message)

# Correct: calling the function to access the scoped variable
print(greet("Alice"))

Additional Solutions

Here are a few additional solutions that may help you fix the “NameError: name ‘plot_cases_simple‘ is not defined” error:

[Fixed]: IndexError: invalid index to scalar variable in Python

  • Make sure you have correctly installed and imported all necessary packages and modules.
  • Check for typos or syntax errors in your code.
  • Make sure you are using the correct version of Python for your code (e.g., Python 2 vs. Python 3).

I hope these solutions and examples help you fix the “NameError: name ‘plot_cases_simple’ is not defined” error in your Python code. Remember to always check for typos, make sure you have imported all necessary modules, and access variables and functions after they have been defined.

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