Okay: time to start doing a little coding on your own. This session is fairly simple, but a few of these questions hint at topics to come in later chapters. Remember, check Appendix C, for the answers; they sometimes contain supplemental information not discussed in the chapters. In other words, you should peek, even if you can manage to get all the answers on your own.
Interaction. Start the Python command line, and
type the expression: "Hello World!"
(including the
quotes). The string should be echoed back to you. The purpose of this
exercise is to get your environment configured to run Python. You may
need to add the path to the python
executable to
your PATH
environment variable. Set it in your
.cshrc or .kshrc file to
make Python permanently available on Unix systems; use a
setup.bat or autoexec.bat
file on Windows.
Programs. With the text editor of your choice,
write a simple module file—a file containing the single
statement: print
'Hello
module
world!'
. Store this
statement in a file named module1.py. Now, run
this file by passing it to the Python interpreter program on the
system shell’s command line.
Modules. Next, start the Python command line
and import the module you wrote in the prior exercise. Does your
PYTHONPATH
setting include the directory where the
file is stored? Try moving the file to a different directory and
importing it again; what happens? (Hint: is there still a file named
module1.pyc in the original directory?)
Scripts. If your platform supports it, add the
#!
line to the top of your
module1.py module, give the file executable
privileges, and run it directly as an executable. What does the first
line need to contain?
Errors. Experiment with typing mathematical
expressions and assignments at the Python command line. First type
the expression: 1
/
0
; what happens? Next, type a variable name you
haven’t assigned a value to yet; what happens this time? You
may not know it yet, but you’re doing exception processing, a
topic we’ll explore in depth in Chapter 7.
We’ll also see Python’s source debugger,
pdb
, in Chapter 8; if you
can’t wait that long, either flip to that chapter, or see other
Python documentation sources. Python’s default error messages
will probably be as much error handling as you need when first
starting out.
Breaks. At the Python command line, type:
L = [1, 2] L.append(L) L
What happens? If you’re using a Python version older than 1.5.1, a Ctrl-C key combination will probably help on most platforms. Why do you think this occurs? What does Python report when you type the Ctrl-C key combination? Warning: if you have a Python older than release 1.5.1, make sure your machine can stop a program with a break-key combination of some sort before running this test, or you may be waiting a long time.