python - Effect of using sys.path.insert(0, path) and sys.path(append) when loading modules

Question

I was recently having a problem with a python ImportError, where the module was found when running on my local computer but not found on the CI server. I solved this problem by swapping sys.path.append(path) in my script with sys.path.insert(0, path) where path is the string module location.

Since this is my module and not an installed package (related question), why does the order of paths fix this problem?

Answer 1

I'm quite a beginner in Python and I found the answer of Anand was very good but quite complicated to me, so I try to reformulate :

1) insert and append methods are not specific to sys.path and as in other languages they add an item into a list or array and :
* append(item) add item to the end of the list,
* insert(n, item) inserts the item at the nth position in the list (0 at the beginning, 1 after the first element, etc ...).

2) As Anand said, python search the import files in each directory of the path in the order of the path, so :
* If you have no file name collisions, the order of the path has no impact,
* If you look after a function already defined in the path and you use append to add your path, you will not get your function but the predefined one.

But I think that it is better to use append and not insert to not overload the standard behaviour of Python, and use non-ambiguous names for your files and methods.