Explanation of NameError: name ‘history’ is not defined
A NameError is a common error in Python which occurs when a name (variable or function) is not defined or not recognized in the current scope. This means that the Python interpreter cannot find the specified name in the program. The error message, “name ‘history’ is not defined“, specifically refers to the name ‘history’ not being defined or declared.
This error typically occurs in the following scenarios:
- Variable not defined: If you receive a NameError related to a variable, it means that the variable has not been assigned a value or has not been declared before its usage.
- Function not defined: If you receive a NameError related to a function, it means that the function has not been defined or declared before its usage.
Example 1: Variable not defined
x = 10
print(y) # NameError: name 'y' is not defined
In this example, the variable ‘x’ is defined and assigned a value of 10. However, the variable ‘y’ is not defined or declared before trying to print its value. As a result, a NameError is raised and it states that ‘y’ is not defined.
Example 2: Function not defined
def add_numbers(a, b):
return a + b
result = multiply_numbers(2, 3) # NameError: name 'multiply_numbers' is not defined
print(result)
In this example, the function ‘add_numbers’ is defined and can be used to perform addition. However, the function ‘multiply_numbers’ is not defined or declared before trying to call it with arguments ‘2’ and ‘3’. Hence, a NameError is raised stating that ‘multiply_numbers’ is not defined.
Solution:
To resolve the NameError, you need to ensure that the name (variable or function) is defined or declared before its usage. This can be done by assigning a value to the variable or defining the function before using it in your program.
Example of fixing NameError:
x = 10
y = 5
print(x + y) # Output: 15
def multiply_numbers(a, b):
return a * b
result = multiply_numbers(2, 3)
print(result) # Output: 6
In this example, the variable ‘x’ and ‘y’ are defined before performing addition. Additionally, the function ‘multiply_numbers’ is defined before calling it with arguments ‘2’ and ‘3’ for multiplication. Hence, no NameError will occur in this updated code.