Nested modules

You can define modules inside of other modules. A directory algorithms holding files sort.py and search.py will generate a module algorithms with sub-modules algorithms.sort and algorithms.search.

To make sure that Python treats such directories correctly, you should create a file __init__.py in the directory. The __init__.py file can be empty; ours prints out “Loading algorithms!”. Notice how many times it prints—when you add an import, does it print again, or no?

In the example below, we’ve started out building the directory algorithms and the search.py module, along with a main.py that imports from both the algorithms.search and algorithms.sort modules. Create the sort.py file with the definition mergesort; change main.py to import that definition.

Paste the following code into algorithms/__init__.py:

print("Loading algorithms!")

Paste the following code into algorithms/search.py:

def linear_search(v, l):
    i = 0
    for x in l:
        if x == v:
            return i
        i = i + 1
    raise ValueError(f'{v} not found')

def binary_search(v, l):
    lo = 0
    hi = len(l) - 1
    while lo <= hi:
        mid = lo + ((hi - lo) // 2) # what goes wrong if we use / ?
#        print(f'looking at {mid} between {lo} and {hi}')
        x = l[mid]
        if   v == x: return mid
        elif v <  x: hi = mid - 1
        elif v >  x: lo = mid + 1
    raise ValueError(f'{v} not found')

Complete sort.py and main.py