Library import

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A while ago I had a question about importing libraries (here: Why should we import Messagebox explicitly into Tkinter even importing with the asterisk?) and explained to me that, in that particular case, import using from <module> import * would not work.

Today I am again with the same doubt, studying some programs here I came across the following form of library import:

from math import ceil
from math import sqrt

Now, wouldn’t it be easier just to use:

from math import *

In this case, other than the one quoted in my other question, use from math import * would import the ceil() and also the sqrt() at once.

So I ask: Is there any advantage in importing only the two specific functions that will be used instead of importing the entire library?

python python-3.x

2 answers

2


There are some advantages, yes.

  1. Does not pollute the local scope;

One of the great advantages of modularizing code is separating things into different scopes, so you have the freedom to work on your project without worrying about conflicting function names. To care about from <module> import * you will be importing all that is stated in __all__ module or all if the module does not define this structure and therefore in this way you have no control over your own scope, which is terrible.

  1. The code doesn’t get magical;

Although in Python many things seem to be simple as magic step, at this point is not interesting. As commented in item (1), when doing from <module> import * You have no control over the scope, so you can’t know what is declared. The consequence of this is that by reading the code you can read something like:

from A import *
from B import *
from C import *

...
x = get_answer()  # 42

And then, where the function was defined get_answer? You can even go after the documentation of modules A, B and C, but look at the resource you need to invest in it just to know where the function comes from, while from C import get_answer eliminates any obscurity of the code.

  1. Ides thank;

Just as in (2) you will suffer to determine where the function was defined, the IDE, considering that it has the tools, will also suffer to understand where it was defined. In many cases she won’t even be able to solve the scope when done from <module> import *, then every function or variable that uses the module the IDE won’t be able to measure if it actually exists, if the function call matches its signature, etc. Probably tools that check typing, like Mypy, will also suffer from it.

Also, you don’t need to duplicate the line; you can include more than one structure with the same import:

from math import ceil, sqrt

1

Advantage would be the final result in size and loading.

Example when you matter ceil and sqrt, va will generate only these packages, case use the * will matter the entire library(not always depends on the library) of the math.

But this may depend on the IDE as well, because some Ides already do this "removal" process where only the packages being used or referenced are generated in the build, removing all "junk" that is not used.

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