Скачать или смотреть How to Modify a Python Script to Use an External File as Input in Command Line

Learn how to adjust your Python scripting skills by modifying a script to read data from an external file through command line inputs, enabling dynamic calculations based on different input files.
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This video is based on the question https://stackoverflow.com/q/64689373/ asked by the user 'Syds148' ( https://stackoverflow.com/u/14580314/ ) and on the answer https://stackoverflow.com/a/64689675/ provided by the user 'Erick Shepherd' ( https://stackoverflow.com/u/8685423/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Modifying Your Python Script for Dynamic File Input

As you venture into the world of Python programming, you may encounter situations where your script needs to process data from different files based on user input. If you've ever wondered how to adapt a Python script to read from an external file via command line, you’re in the right place! This guide will guide you step-by-step through this process, ensuring that you can efficiently use your scripts for various data files.

The Problem

You have a Python script named Shannon_readfile.py that is intended to perform some calculations based on numerical values stored in a text file. Your goal is to modify it so that you can specify different filenames directly in the command line when running the script. This will allow the script to process different datasets without requiring changes to the codebase itself.

Expected Command Line Usage

You should be able to run the following commands in the terminal:

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Solution Overview

To modify the script, the following changes are necessary:

Import Necessary Libraries: Ensure you have the required libraries.

Read Command Line Arguments: Utilize sys.argv to retrieve the filename from the command line.

Read File Contents: Open the specified file and read its lines into a list.

Perform Calculations: Update your script to calculate values based on the data read from the file.

Step-by-Step Guide

Here’s how you can make the modifications to your Shannon_readfile.py script:

1. Import Required Libraries

Ensure you have the needed libraries at the beginning:

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2. Retrieve the Filename from Command Line

Use the sys.argv list to get your filename parameter:

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3. Read the Input File

Open the specified file and read its contents into a list P:

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This reads every line from the provided file, assuming it contains one numerical value per line.

4. Initialize Variables and Perform Calculations

Next, initialize your computation variables and update the logic for calculating N and H:

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5. Print the Results

Finally, print the computed values:

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Complete Code Example

Here's how your final script should look after these modifications:

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Conclusion

By following the steps above, you’ve successfully modified your Python script to read from an external file specified in the command line. This enhancement will not only streamline your workflow but also allow for more flexible data manipulation based on different datasets. Keep practicing and experimenting with your scripts, and soon you'll become very adept at programming with Python!