Python: importing a module

Question

Suppose I have a python fibo.py model defined 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 .. drag the translator:

 >>> 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 was expecting an error as I only imported fib and fib2. But I don’t understand why the expression was printed when I imported only 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 the expected behavior. When you import using from X import Y , the module is still loading and executing as described in the Language Reference . In fact, when you do

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

prints This is a statement , and then foo . The second import does not print anything since the module is already cached.

The second module will print This is a statement , and then fibo . The module knows its name at boot time.

Answer 2

Python must load the entire module in order to import anything from it. Python imports the entire module into the module’s cache, but only the characters you display are visible to you. (If you import a second time, it will not start because the module is cached on the first import.)