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<FONT><h3>Code Examples</h3>
<p>This application subclasses an exception class and executes the commands stored in a file. The filename is asked by the application.</p>
<H5>
Listing 5.1 Configuration File (File configfile.py)</H5>
<PRe claSS="monofont">
1: ###
2: # Program: Configuration File
3: # Author: Andre S Lessa
4: ###
5:
6: ### import modules
7:
8: import exceptions, sys
9:
10: configfile = raw_input("Configuration File: ")
11:
12: class ConfigError (exceptions.Exception):
13: def __init__(self, arg=None):
14: self.args = arg
15:
16: try:
17: try:
18: file = open(configfile)
19: lines = file.readlines()
20: finally:
21: file.close()
22: except:
23: print "Error. Invalid file name."
24: sys.exit()
25:
26: lines[0] = lines[0][:-1]
27:
28: if lines[0] != "CFG2000":
29: raise ConfigError, "Invalid header."
30:
31: lines = lines[1:]
32:
33: for line in lines:
34: try:
35: exec line
36: except LookupError, b:
37: if b.args[0] == "list index out of range":
38: print "Error. Invalid index entry"
39: else:
40: print "Error. Generic LookupError entry"
41: except SystemExit:
42: print "Error. sys.exit() cannot be used."
</PRe>
<p>Lines 12-14: The class <tt CLASs="monofont">ConfigError</tt> is created. It inherits all the attributes from the <tt class="monofont">exceptions.Exception</tt> class.</p>
<p>Line 29: Raises our new exception class.</p>
<p>In order to test this program, we have to create a file called <tt clAss="monofont">config.txt</Tt> that contains the following lines:</p>
<pRe>
CFG2000
print
print "Configuration File"
print "------------------"
server = "SRV001"
port = 80
print "Server: ", server
print "Port: ", port
</pre>
<P>The next interaction shows how to call the program. It also shows the results provided by the program when no exception is raised.</p>
<prE>
C:\ Python>python configfile.py
Configuration File: config.txt
Configuration File
------------------
Server: SRV001
Port: 80
C:\ Program Files\ Python>
</PRE>
<p>This simple program creates a class structure that stores and prints a list of groceries.</p>
<h5>
Listing 5.2 Groceries List (File groceries.py)</h5>
<PRE Class="monofont">
1: ###
2: # Program: Groceries List
3: # Author: Andre S Lessa
4: ###
5:
6: ### import modules
7:
8:
9: class grocery:
10: "Items that you need to buy at the grocery store."
11: def __init__(self, name, quantity=1):
12: self.name = name
13: self.quantity = quantity
14:
15: items = { }
16: print "Type ENTER when you are done."
17: while 1:
18: name = raw_input("Grocery name: ")
19: if name == "":
20: break
21: quantity = raw_input("%s quantity: " % (name))
22: if quantity == "":
23: items[name] = grocery(name)
24: else:
25: items[name] = grocery(name,quantity)
26:
27: print "------------------------\ nList of groceries to buy"
28: print "------------------------"
29:
30: for item in items.keys():
31: print "Grocery : ", items[item].name,
32: print "\ tQuantity: ", items[item].quantity
33:
34: print "---------"
</PRE>
<P>Line 9: Declares the <tt clASS="monofont">grocery</Tt> class.</p>
<p>Line 10: The class's documentation text.</p>
<p>Line 11: A default value is defined for the <tt class="monofont">quantity</tt> argument.</p>
<p>Lines 22-25: Uses a different interface to initialize the object, depending on the information provided.</p>
<p>Lines 31-32: Provides access to the object attributes.</p>
<p>The next interaction shows how the program works.</P>
<prE>
C:\ Python>python groceries.py
Type ENTER when you are done.
Grocery name: bananas
bananas quantity: 12
Grocery name: apples
apples quantity: 6
Grocery name: pears
pears quantity: 8
Grocery name: pineapple
pineapple quantity:
Grocery name:
------------------------
List of groceries to buy
------------------------
Grocery : pineapple Quantity: 1
Grocery : pears Quantity: 8
Grocery : apples Quantity: 6
Grocery : bananas Quantity: 12
---------
C:\ Python>
</pre>
<P>This file introduces two classes and one function that extensively manipulate class methods and attributes.</p>
<h5>
Listing 5.3 Company employees (File company.py)</h5>
<pRe clASS="monofont">
1: ###
2: # Program: Company employees
3: # Author: Andre S Lessa
4: ###
5:
6: ### import modules
7:
8: import types
9:
10: class Employee:
11: "Generic class for all company employees"
12:
13: __employees = 0
14:
15: def __init__(self,name,salary=500.00):
16: self.name = name
17: self.salary = salary
18: self.family = []
19: Employee.__employees = Employee.__employees + 1
20:
21: def __str__(self):
22: return "employee: %s" % self.name
23:
24: def raisesalary(self, percent):
25: self.salary = self.salary + (self.salary * (1.0/percent))
26:
27: def job(self):
28: print self.name, "writes Python code."
29:
30: def hasfamily(self):
31: return len(self.family) > 0
32:
33: def addmember(self, name):
34: self.family.append(name)
35:
36: def removemember(self, arg):
37: if len(self.family) > 0:
38: if type(arg) == type(1):
39: self.removemember_int(arg)
40: elif isinstance(arg, types.StringType):
41: self.removemember_str(arg)
42:
43: def removemember_int(self, index):
44: member = self.family[index]
45: del self.family[index]
46: return member
47:
48: def removemember_str(self, name):
49: for member in self.family:
50: if member == name:
51: del self.family[self.family.index(member)]
52: return member
53:
54: def __getitem__(self, index):
55: member = self.family[index]
56: return member
57:
58: class Leader(Employee):
59: "Company's Leader of the employees"
60: def __init__ (self, name):
61: Employee.__init__ (self, name, 1500.00)
62: def job(self):
63: print self.name, "supervises who writes Python code."
64:
65: def totalemployee():
66: return Employee._employee_employees
</Pre>
<p>Line 10: Defines the <tT CLAss="monofont">Employee</tt> class.</P>
<P>Line 13: Class variable <TT clasS="monofont">__employees.</TT></P>
<p>Line 19: Increments the number of employees.</p>
<p>Line 31: Returns a logical value (<tt class="monofont">0</tt> or <tt class="monofont">1</tT>).</p>
<p>Lines 36-41: Implements polymorphism by enabling the user to enter both string and integer values.</P>
<p>Lines 43-52: Helper methods for the polymorphism implementation.</p>
<p>Line 54: Enables the slicing of employees instances.<A name="idx1073743522"></A><a naME="idx1073743523"></A><A name="idx1073743524"></A><A NAme="idx1073743525"></a><a NAME="idx1073743526"></a></p>
<p>Line 58: Defines a subclass Leader that inherits attributes from the <tT CLAss="monofont">Employee</tt> class.</p>
<p>Lines 60-63: The <tt class="monofont">__init__()</tt> and the <tt claSs="monofont">job()</tT> methods are overwritten.</p>
<p>Line 65: Provides a function that returns the total number of employees who are currently part of the class.</p>
<P>The following interaction shows how the classes must be used.</p>
<pre>
>>> import company
>>> andre = company.employee("Andre") # Creates an employee instance
>>> print andre
employee: Andre
>>> print andre.salary
500
>>> andre.raisesalary(10) # Raises his salary in 10 percent
>>> andre.salary
550.0
>>> andre.job() # Shows his job description
Andre writes Python code.
>>> andre.hasfamily()
0
>>> andre.addmember("Renata") # Add a member to his family
>>> andre.addmember("Joao Pedro") # Add a member to his family
>>> andre.addmember("Rebecca") # Add a member to his family
>>> andre.hasfamily() # Returns 1 or 0
1
>>> andre.family
['Renata', 'Joao Pedro', 'Rebecca']
>>> andre.removemember("Joao Pedro") # Remove string member from list
>>> andre.family
['Renata', 'Rebecca']
>>> andre.removemember("Renata
>>> andre.family
['Rebecca']
>>> andre.removemember(0) # Remove index member from list
>>> andre.family
[]
>>> andre.addmember("Joao Pedro")
>>> andre.addmember("Renata")
>>> andre.addmember("Rebecca")
>>> andre[0]
'Joao Pedro'
>>> andre[1
'Renata'
>>> andre[2]
'Rebecca'
>>> company.totalemployee()# Shows the total number of employees
1
>>> renata = company.employee("Renata")
>>> company.totalemployee()
2
>>> Joao = company.Leader("Joao Pedro") # Creates a leader instance
>>> Joao.salary
1500.0
>>> Joao.job()
Joao Pedro makes food
>>> company.totalemployee()
3
>>>
</Pre>
</fONT>
<P><TABLE width="100%" border=0><TR valign="top"><TD><font size=1 color="#C0C0C0"><br></font></TD><TD align=right><font size=1 color="#C0C0C0">Last updated on 1/30/2002<br>Python Developer's Handbook, © 2002 Sams Publishing</font></TD></TR></TABLE></P>
<TABLE border=0 width="100%" cellspacing=0 cellpadding=0><TR><td align=left width="15%" class="headingsubbarbg"><a href="113.html" title="Summary"><font size="1">< BACK</font></a></td><td align=center width="70%" class="headingsubbarbg"><font size="1"><a href="popanote.asp?pubui=oreilly&bookname=0672319942&snode=114" target="_blank" title="Make a public or private annnotation">Make Note</a> | <a href="114.html" title="Use a Safari bookmark to remember this section">Bookmark</a></font></td><td align=right width="15%" class="headingsubbarbg"><a href="116.html" title="II: Advanced Programming"><font size="1">CONTINUE ></font></a></td></TR></TABLE>
</TD></TR></TABLE>
<br><TABLE width=100% bgcolor=white border=0 cellspacing=0 cellpadding=5><TR><TD><H4 class=Title>Index terms contained in this section</H4>
<font size=2>
code<BR>
<a href="#idx1073743522">company employees</a><BR>
company employees<BR>
<a href="#idx1073743524">source code</a><BR>
employees<BR>
<a href="#idx1073743525">source code</a><BR>
lists<BR>
company employees<BR>
<a href="#idx1073743526">source code</a><BR>
source code<BR>
<a href="#idx1073743523">company employees</a><BR>
<BR>
</font></TD></TR></TABLE>
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