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Exercises/ex1_6.md

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+\[ [Index](index.md) | [Exercise 1.5](ex1_5.md) | [Exercise 2.1](ex2_1.md) \]
+
+# Exercise 1.6
+
+*Objectives:*
+
+- Defining modules
+- Using the import statement
+
+*Files Created:* None
+
+**Note:**
+For this exercise involving modules, it is
+critically important to make sure you are running Python in a proper
+environment.  You may need to check the value of `sys.path` if you 
+can't get import statements to work.  Ask for assistance if everything
+seems broken.
+
+Before starting this exercise, first restart your Python interpreter session.  If using IDLE, click on
+the shell window and look for a menu option "Shell > Restart Shell".   You should get a message like this:
+
+```python
+>>> ##################== RESTART ##################==
+>>> 
+```
+
+If you are using Unix, simply exit Python and restart the interpreter.
+
+## (a) Using the import statement
+
+In previous exercises, you wrote two programs `pcost.py` and
+`stock.py`.   Use the `import` statement to load these
+programs and use their functionality:
+
+```python
+>>> import pcost
+44671.15
+>>> pcost.portfolio_cost('Data/portfolio2.dat')
+19908.75
+>>> from stock import Stock
+>>> s = Stock('GOOG', 100, 490.10)
+>>> s.name
+'GOOG'
+>>> s.cost()
+49010.0
+>>>
+```
+
+If you can't get the above statements to work, you might have placed
+your programs in a funny directory.  Make sure you are running Python
+in the same directory as your files or that the directory is included
+on `sys.path`.
+
+
+## (b) Main Module
+
+In your `pcost.py` program, the last statement called a
+function and printed out the result.  Modify the program so that this
+step only occurs if the program is run as the main program.  Now,
+try running the program two ways:
+
+First, run the program as main:
+
+```
+bash % python3 pcost.py
+44671.25
+bash %
+```
+
+Next, run the program as a library import.  You should not see any
+output.
+
+```python
+>>> import pcost
+>>>
+```
+
+\[ [Solution](soln1_6.md) | [Index](index.md) | [Exercise 1.5](ex1_5.md) | [Exercise 2.1](ex2_1.md) \]
+
+----
+`>>>` Advanced Python Mastery  
+`...` A course by [dabeaz](https://www.dabeaz.com)  
+`...` Copyright 2007-2023  
+
+![](https://i.creativecommons.org/l/by-sa/4.0/88x31.png). This work is licensed under a [Creative Commons Attribution-ShareAlike 4.0 International License](http://creativecommons.org/licenses/by-sa/4.0/)