Deitel - Python, How To Program.pdf

Pythonhtp1_04.fm Page 147 Saturday, December 8, 2001 9:34 AM
Chapter 4 Functions 147
11 if CGI == "yes":
12 print "CGI scripts are enabled"
13 print # prints a new line
14
15 generateWebsite( "Deitel" )
16
17 generateWebsite( "Deitel", Flash = "yes",
18 url = "www.deitel.com/new" )
19
20 generateWebsite( CGI = "no", name = "Prentice Hall" )
Generating site requested by Deitel using url www.deitel.com
CGI scripts are enabled
Generating site requested by Deitel using url www.deitel.com/new
Flash is enabled
CGI scripts are enabled
Generating site requested by Prentice Hall using url www.deitel.com
Fig. Fig. 4.21 4.21 Keyword parameters. (Part 2 of 2.)
Function generateWebsite takes four arguments. The keyword argument names
url, Flash and CGI are assigned the default values "www.deitel.com", "no" and
"yes", respectively (lines 4–5). The function identifies who is requesting the Web site and
displays a message if the Web site is Flash- or CGI-enabled (lines 6–13).
The function call in line 15 passes one argument, a value for name, to function
generateWebsite. The function uses the default values given in the definition for the
other parameters.
The function call in lines 17–18 passes three arguments to generateWebsite.
Variable name again has the value "Deitel". The call also assigns the value "yes" to
keyword argument Flash and "www.deitel.com/new" to keyword argument url.
This function call illustrates that the order of keyword arguments is more flexible than that
of regular arguments in an ordinary function call. The Python interpreter matches the value
"Deitel" with variable name by its position in the function call. The Python interpreter
matches the values passed to url and Flash by their keyword argument names rather
than by their positions in the function call. The value of name must come first in any call
to generateWebsite if it is not referenced by specifying a value for name in the argument
list. Line 20 demonstrates that any function argument can be referenced as a keyword
even if it has no default value.
The interactive session of Fig. 4.22 demonstrates common errors when mixing nonkeyword
and keyword arguments. Function call test( number1 = "two", "Name" )
causes an error, because the non-keyword argument is placed after the keyword argument.
Function call test( number1 = "three" ) is incorrect, because function test expects
one non-keyword argument.
Common Programming Error 4.10
Misplacing or omitting the value for a non-keyword argument in a function call is an error. 4.10