How do you understand other people's code?

Question

Programming

They gave me a project that is almost ready, I did not participate in the development. The project is big. Previously, I had no problems when I wrote projects from scratch. But here, when a bug is fixed, for some reason I can’t figure it out quickly (I don’t have time in time).
How do you deal with other people's code? Is there any technique? Or maybe the problem is me?

Answer 1

Just read the code and try to understand what the author wanted to say.
Try to solve the same problem in your mind and see the differences. Think about the logic behind the differences.
Set breakpoints and see call stacks, compare them.
Understand the domain, what terminology is used, and how it is mapped to code identifiers.
Understand the contracts between parts of the code and which part is not fulfilling its contract.

Answer 2

Slowly and gradually.

Answer 3

Two weeks - a month, usually, they give to enter the project, at this time they talk a lot and do not ask much for performance, then the person enters the project and everything goes fine.