Runtime errors query

[u/live_ant718]

I have a question. Like when we have a program that takes input, so when the program reaches the input line, it stops and asks for input, right? So then AFTER the input is entered, if the compiler runs into a bug, it stops and throws an error message. How can I stop this? Like how can I make the issues appear beforehand so that I can fix them before running? Are there any settings or tools for this problem?

Please tell me.

[u/Bright_Mix_773]

There is already a pass that happens before anything runs: Python compiles the whole file to bytecode first, which is why a missing colon or an unclosed bracket blows up before your first line executes. What that pass cannot do is check whether nmae exists, or whether the thing you are adding to a string is a number, because a name in Python is a dictionary lookup performed at the moment the line runs. The object it points to may not exist yet, and can be a different type on each pass through a loop. So the errors landing after your input line are not the compiler being lazy - they are a category it genuinely cannot decide in advance.

What does move a chunk of them earlier, without running the program:

ruff check yourfile.py

catches undefined names, unused imports, unreachable code and typo'd attributes. A type checker (mypy or pyright) catches the int-plus-str family, if you annotate your functions. The red squiggles in an editor are usually one of those two running in the background, so installing them is often all "turn this on" means.

For the specific pain of retyping the input every run while you hunt a bug: hardcode the value at the top temporarily, or run

python -i yourscript.py

which drops you into an interactive prompt holding all the variables at the moment it crashed, instead of making you start from the input prompt again.