Python: Importing Module

Question

Lets say I have a python model fibo.py defined as below:

#Fibonacci numbers module
print "This is a statement"
def fib(n):
    a,b = 0,1
    while b < n:
        print b
        a, b = b, a+b

def fib2(n):
    a,b = 0,1
    result= []
    while(b < n):
        result.append(b)
        a, b = b, a+b
    return result

In my interpreter session, I do the following:

>> import fibo
This is a statement
>>> fibo.fib(10)
1
1
2
3
5
8

>>> fibo.fib2(10)
[1, 1, 2, 3, 5, 8]
>>> fibo.__name__
'fibo'
>>> 

So far so good... restart the interpreter:

>>> from fibo import fib,fib2
This is a statement
>>> fibo.__name__
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'fibo' is not defined
>>>

I expected the error as I have only imported fib and fib2. But I don't understand why the statement was printed when I only imported fib and fib2.

Secondly if I change the module as:

#Fibonacci numbers module
print "This is a statement"
print __name__

What should be the expected result?

Answer 1

This is expected behavior. When you import with from X import Y, the module is still loaded and executed, as documented in the Language Reference. In fact, when you do

from fibo import fib
print("foo")
import fibo

will print This is a statement, followed by foo. The second import doesn't print anything as the module is already cached.

Your second module will print This is a statement followed by fibo. The module knows its own name at load time.

Answer 2

Python has to load the whole module in order to import anything from it. Python imports the whole module into its module cache, but only the symbols you import are visible to you. (If you import a second time, it will not run; this is because the module is cached the first time it is imported.)