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How to Check Column Nulls and Replace: Pandas

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Here is a post that shows how to count Nulls and replace them with the value you want in the Pandas Dataframe. We have explained the process in two steps - Counting and Replacing the Null values. Count null values (column-wise) in Pandas ## count null values column-wise null_counts = df.isnull(). sum() print(null_counts) ``` Output: ``` Column1    1 Column2    1 Column3    5 dtype: int64 ``` In the above code, we first create a sample Pandas DataFrame `df` with some null values. Then, we use the `isnull()` function to create a DataFrame of the same shape as `df`, where each element is a boolean value indicating whether that element is null or not. Finally, we use the `sum()` function to count the number of null values in each column of the resulting DataFrame. The output shows the count of null values column-wise. to count null values column-wise: ``` df.isnull().sum() ``` ##Code snippet to count null values row-wise: ``` df.isnull().sum(axis=1) ``` In the above code, `df` is the Panda

The Quick and Easy Way to Fix Python UnboundLocalError

Here is the easy way to fix the issue of the Python UnboundLocalError, allowing users to resolve any problems quickly.


UnboundLocalError



Python UnboundLocalError

While the variable in the function has already been defined, during execution, the result prints with an error of UnboundLocalError. Below, you will find an example that explains the issue and resolution.

Error: file 'example.txt' not found
Traceback (most recent call last):
File "main.py", line 16, in <module>
open_file("example.txt")
File "main.py", line 11, in open_file
if f:
UnboundLocalError: local variable 'f' referenced before assignment


** Process exited - Return Code: 1 **

Press Enter to exit terminal


Python program using try, except and finally

Below program explains how to use try, except and finally blocks in python. But during the execution, it prints UnboundLocalError.


Program using try, except and finally

# Define a function that may raise an exception
def open_file(filename):
    try:
        f = open(filename, "r")
        contents = f.read()
    except FileNotFoundError:
        print(f"Error: file '{filename}' not found")
    else:
        print(f"Contents of file '{filename}':\n{contents}")
    finally:
        if f:
            f.close()
            print(f"File '{filename}' has been closed.")

# Call the function with a valid filename
open_file("example.txt")

# Call the function with an invalid filename
open_file("invalid.txt")


The output:

Error: file 'example.txt' not found
Traceback (most recent call last):
  File "main.py", line 16, in <module>
    open_file("example.txt")
  File "main.py", line 11, in open_file
    if f:
UnboundLocalError: local variable 'f' referenced before assignment


** Process exited - Return Code: 1 **
Press Enter to exit terminal

Resolution for UnboundLocalError

In the function, before the try block, add f = None. That resolves the issue. Here is the corrected program.

Corrected program

# Define a function that may raise an exception
def open_file(filename):
    try:
        f = None
        f = open(filename, "r")
            contents = f.read()
    except FileNotFoundError:
        print(f"Error: file '{filename}' not found")
    else:
        print(f"Contents of file '{filename}':\n{contents}")
    finally:
        if f:
            f.close()
            print(f"File '{filename}' has been closed.")

# Call the function with a valid filename
open_file("example.txt")

# Call the function with an invalid filename
open_file("invalid.txt")


The output is:

Error: file 'example.txt' not found
Error: file 'invalid.txt' not found


** Process exited - Return Code: 0 **
Press Enter to exit terminal


Summary

  • Return statement not coded in the function. As a result, it gave UnboundLocalError.
  • A function returns the None object by default if the control flow falls off the end of the function body without running into a return statement.

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