Скачать или смотреть Why does Python's print() function add a % at the end of output when using the end parameter?

Discover why the Python `print()` function might display a pesky `%` at the end of your output, and learn how to fix this common shell interaction issue.
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Understanding the % Symbol in Python's print() Function Output

When working with the Python programming language, particularly in output handling, you might encounter unexpected behavior that can leave you scratching your head. One common issue is when using the print() function along with the end parameter, and noticing a % appear at the end of the print output. If you've found yourself puzzled by this, you are not alone. Below, we'll explore why this happens and how to address it in your coding practices.

The Problem: Unexpected Output

You may have written a code snippet to simulate a lotto draw in Python, using the print() function to display the results on one line without spaces. Your intention was to create a seamless presentation of the drawn numbers and letters, but instead, you encountered a % symbol at the end of your output. Here’s an example of a code causing this issue:

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

Despite using end='' in the print() function to prevent new line characters after each output, you notice a % at the end when executed. So, what's behind this behavior?

The Solution: Identifying the Source of the %

First and foremost, it's crucial to note that the unexpected % does not originate from Python itself, but from your shell. This can be due to two main causes:

Shell Prompt Behavior: If no final line feed (newline character) is generated by your code, the shell prompt appears directly after your printed output, resulting in the % being displayed immediately after your output.

Specific Shells (Fish or Zsh): Some shells, like Fish or Zsh, modify how prompts appear. When using the print() function with end='', these shells may add a % sign to indicate that something unexpected has occurred due to the absence of a final line feed. This ensures you are aware that your output isn't behaving as conventionally expected.

Example Scenarios

sh/ksh/bash

Output may look like this:

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

The shell prompt is directly tacked at the end of the output.

Zsh/Fish

Output may look like this:

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

The prompt remains in its usual position while notifying you of the unusual behavior by adding a %.

Final Thoughts

To eliminate the % symbol from appearing uninvited at the end of your output, consider adding a final print statement without arguments after your loop to generate a newline. Here’s how you could modify your original code:

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

Now you can print your lotto results without any trailing symbols, and your shell prompt will behave as intended, without interruption.

By understanding the interaction between your Python code and the shell environment, you can create cleaner and more professional outputs. This knowledge empowers you to write more effective Python scripts in your programming journey.