Скачать или смотреть How to Convert a String Expression to a List in Python Without Using Built-in Functions or Regex

Learn how to convert a string mathematical expression into a structured list in Python without relying on built-in functions or regular expressions. Perfect for beginners!
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This video is based on the question https://stackoverflow.com/q/68829551/ asked by the user 'delux' ( https://stackoverflow.com/u/7659421/ ) and on the answer https://stackoverflow.com/a/68829745/ provided by the user 'Andrej Kesely' ( https://stackoverflow.com/u/10035985/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Converting a String Expression to a List in Python

When working with mathematical expressions in programming, it’s often necessary to convert these expressions into a structured format. In Python, converting a string representation of an expression—like "(52^2)+ 150-(2^2+ 4+ 5)"—into a list can be challenging, especially if you’re looking to do it without using built-in functions or regular expressions (regex). Here, we'll walk through a straightforward solution that breaks down the string into its components.

The Problem

You have a string expression that combines numbers, operators, and parentheses, and you want to split this string into individual elements in a list. For instance, the example expression "(52^2)+ 150-(2^2+ 4+ 5)" should be converted into:

[[See Video to Reveal this Text or Code Snippet]]

The challenge comes from wanting to avoid Python's built-in functions like .split() or using regex, which generally simplifies this process.

The Solution

To convert the string expression effectively, we can iterate through each character in the string and separate numbers from operators and parentheses manually. Below is a simple function that achieves this:

Step-by-Step Breakdown

Initialize a buffer: This will temporarily hold digits that are part of a number.

Iterate through each character: As you loop through the string, you'll check:

If the character is a digit (0-9), append it to the buffer.

If the character is not a digit:

If there's a number in the buffer, yield the number and reset the buffer.

Yield the current character (operator or parenthesis).

Empty the buffer: After the loop, if there’s still a number in the buffer (e.g., at the end of the string), yield that as well.

The Code

Here’s the complete Python code to achieve the conversion:

[[See Video to Reveal this Text or Code Snippet]]

Output

When you run the above code, it will produce the following list:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following the approach outlined here, you can efficiently convert a string expression into a structured list in Python without relying on built-in functions or regex. This method not only reinforces your understanding of string manipulation in Python but also shows how to tackle problems with creative coding solutions.

Now, go ahead and try this method with your own expressions! Happy coding!