Download Python - ReportLab

Extreme Testing, Integration and
Sandwiches with Python
Andy Robinson
CEO / Chief Architect, ReportLab Inc.
BCS OOPS
3 July 2002
Part 1
Introduction
What is Python?
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High level, object oriented scripting language
Open Source
Cross-platform - based on Ansi C or Java
Cross-platform GUI and DB libraries
very easy to read
very dynamic
What is used for?
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Friendly alternative to Perl
Quick and dirty scripting
CGI scripts
Large scale application development
Integrating other systems
Python as an Integration Tool
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Good with files
Dynamic or static linking to C-based languages
Great COM support
CORBA etc.
Great networking libraries
Great Java integration
"Low-threat" uses in the corporate world
...or how to get the boss to say "Yes"
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Adding a macro language to applications
Rapid Prototyping of object models and algorithms
Building test harnesses for other systems
Data Cleaning and Transformation
Python as Glue
Getting Popular....
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500,000+ users
15+ books
Used at NASA, Yahoo, Red Hat, Infoseek, Industrial Light and
Magic, IBM, Fidelity Investments and many more
Part 2 - The Python Environment
Where to get it - http://www.python.org/
What you get
Windows distribution as an example (CD available today)
• Python 2.0 - command line program
• Full documentation
• Windows extensions - GUI and COM support
Many competing IDEs now available.
Demo time...
Python core on Windows
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python20.dll - 652kb, the language, exports almost everything
python.exe - 5kb console mode program
pythonw.exe - 21kb non-console mode program - avoids ugly
black DOS boxes when you don't want standard input/output
File Types
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.py - python source (.java)
.pyc - byte-compiled, rebuilt on demand (.class)
.pyd - DLL with a Python-specific entry point
Part 3
A Crash Course in Python
Hello World
PythonWin 2.1.3 (#35, Apr 8 2002, 17:47:50) [MSC 32 bit (Intel)] on
win32.
Portions Copyright 1994-2001 Mark Hammond ([email protected]) see 'Help/About PythonWin' for further copyright information.
>>> print 'hello world'
hello world
Contrast that to C++ or Java
Numbers, Strings and Variables
>>> 2+2
4
You can assign to variables with '=' :
>>>
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3
>>>
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6
>>>
x=3
x
y=x*2
y
Python supports all standard arithmetical operators :
>>> 22/7
3
>>> 22.0/7.0
3.1428571428571428
>>>
Complex numbers are supported using the letter j :
>>> (3 + 1j) * (3 -1j)
(10+0j)
>>>
Strings can be wrapped in double or single quotes:
>>> greeting = 'hello'
>>> epithet = "stranger"
They can be concatenated (using '+') and repeated (using '*'):
>>> greeting + ", " + epithet
'hello, stranger'
>>> "spam" * 10
'spamspamspamspamspamspamspamspamspamspam'
>>>
Lists
Lists are wrapped in square brackets.
They can contain any Python objects.
>>> mylunch = ['spam', 'eggs', 'guiness', 'raspberries',
'wafer-thin mint']
>>> mylunch[0]
'spam'
>>> mylunch[1:3], mylunch[-1]
(['eggs', 'guiness'], 'wafer-thin mint')
>>>
Tuples
Parentheses indicate a tuple.
Tuples are similar to lists but can't be modified once created.
>>> mylunch[2] = 'tea'
>>> mylunch
['spam', 'eggs', 'tea', 'raspberries', 'wafer-thin mint']
>>> meal_deal = ('burger', 'fries', 'coke')
# a tuple
>>> meal_deal[1] = 'onion rings'
Traceback (most recent call last):
File "<interactive input>", line 1, in ?
TypeError: object doesn't support item assignment
>>>
Control Structures
The For Loop
The for loop operates over lists not numbers:
>>> for item in mylunch:
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print item
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spam
eggs
tea
raspberries
wafer-thin mint
>>>
The While Loop
>>> x = 2
>>> while x < 50:
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x = x * 2
...
print x
...
4
8
16
32
64
>>>
If and Else
The else clause is optional:
>>> if 'chocolate' in mylunch:
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print "that's not allowed"
... else:
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print "enjoy your meal"
...
enjoy your meal
>>>
Elif
You can also have a number of intermediate elif (else-if) clauses.
Something like switch or case in other languages.
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>>>
salary = 20000
if salary < 4000:
tax_rate = 0
elif salary < 29000:
tax_rate = 0.25
elif salary < 100000:
tax_rate = 0.4
else:
emigrate()
# that's a function call
Functions
>>> def double(x):
...
return x * 2
...
>>> double(2)
4
>>> def first_and_last(aList):
>>> def first_and_last(aList):
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return(aList[0], aList[-1])
...
>>> first_and_last(range(5))
(0, 4)
>>> def sayHello():
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print 'hello'
...
>>> sayHello()
hello
>>>
Functions with default arguments
>>> def makeCoffee(size, milk=None, sugar=None):
...
order = 'one ' + size + ' coffee'
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if milk and sugar:
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order = order + ' with milk and sugar'
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elif milk:
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order = order + ' with milk'
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elif sugar:
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order = order + ' with sugar'
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else:
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pass # pass means 'do nothing'
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return order
...
>>> makeCoffee('large')
'one large coffee'
>>> makeCoffee('large', 1)
'one large coffee with milk'
>>> makeCoffee('large', milk=0, sugar=1)
'one large coffee with sugar'
>>>
Dictionaries
Dictionaries are based on a hash table.
Lookup time is almost constant.
Enclosed by braces.
Keys and values separated by a colon.
>>> fur_colours = {}
>>> fur_colours['Tinky-Winky'] = 'purple'
>>> fur_colours['Dipsy'] = 'green'
>>> fur_colours['LaLa'] = 'yellow'
>>> fur_colours
{'Tinky-Winky': 'purple', 'Dipsy': 'green', 'LaLa': 'yellow'}
>>> fur_colours['LaLa']
'yellow'
Dictionary Methods
Dictionaries support some useful methods of searching:
by keys, values and whether or not a certain key is present.
>>> fur_colours.keys()
['Tinky-Winky', 'Dipsy', 'LaLa']
>>> fur_colours.values()
['purple', 'green', 'yellow']
>>> fur_colours.items() # converts to a list of tuples
[('Tinky-Winky', 'purple'), ('Dipsy', 'green'), ('LaLa', 'yellow')]
>>> len(fur_colours)
3
>>> fur_colours.has_key('Po')
0
>>>
Modules
Python code is organised into modules.
Some are built into Python, others are stored in external files.
>>> import math
>>> math.sin(math.pi/2)
1.0
>>>
>>> from string import split, join
>>> split('We are the knights who say Ni')
['We', 'are', 'the', 'knights', 'who', 'say', 'Ni']
>>>
Classes
>>> class Car:
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def __init__(self):
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self.milespergallon = 25.0
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self.travelled = 0
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self.color = 'blue'
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self.gas = 20
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def drive(self, miles):
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self.travelled = self.travelled + miles
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self.gas = self.gas - (miles / self.milespergallon)
...
>>> c = Car()
>>> c.drive(100)
>>> c.travelled
100
>>> c.gas
16.0
>>>
Exception Handling
>>> def func1(arg):
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func2(arg)
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>>> def func2(arg):
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func3(arg)
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>>> def func3(arg):
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# this should cause an error
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return arg / 0
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>>> func1(17)
Traceback (most recent call last):
File "<interactive input>", line 1, in ?
File "<interactive input>", line 2, in func1
File "<interactive input>", line 2, in func2
File "<interactive input>", line 3, in func3
ZeroDivisionError: integer division or modulo by zero
>>>
The Except Clause
The except clause can optionally specify particular
error types to look for:
>>> try:
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y_scale_factor = plotheight / (dataMax - dataMin)
... except ZeroDivisionError:
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y_scale_factor = 0
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>>>
The Finally Clause
The try...finally clause always executes the finally section
whether an error occurs or not:
>>> f = open('somefile.dat', 'w')
>>> try:
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# fetch some data
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# store it in the file
... finally:
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f.close() # make sure file is closed
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# even if errors occurred
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Have you noticed...?
...the lack of block delimiters?
'statement grouping is done by indentation instead of begin/end
brackets'
Part 4
Integration with Python
Integration Tools
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DB API
XML
Numerous web protocols inc. SOAP and XML-RPC
Pyro and others
COM
CORBA
Java - Jython, JPE
C/C++ - Python C API, SWIG, CXX, Pyrex...
Python Database APIs
>>> import mx.ODBC.Windows
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conn = mx.ODBC.Windows.connect(DATASOURCE, USER, PASSWORD)
cur = conn.cursor()
cur.execute("""SELECT JobDescriptionId, DocGroupId, Description
FROM RPAJobDescriptions
WHERE UserId = 'alice' ORDER BY DocGroupId""")
data = cur.fetchall()
>>> pprint.pprint(data)
[(6, 'multipagesamples', 'simple multipage doc #1'),
(7, 'multipagesamples', 'simple multipage doc #2'),
(8, 'multipagesamples', 'simple multipage doc #3')]
>>>
XML Parsing
>>> import pyRXP
>>> p=pyRXP.Parser()
>>> p.parse('<tag1><tag2>content</tag2></tag1>')
('tag1', None, [('tag2', None, ['content'], None)], None)
>>>
Reading a URL
import urllib
conn = urllib.urlopen('http://www.reportlab.com/index.html')
print conn.headers
data = conn.read()
Similar high level APIs exist for most internet protocols
Integration with C /C++
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Python C API: extend or embed
SWIG: generate wrappers for C++ code
CXX and Pyrex - newer
COM Clients
>> import win32com.client
>> xl = win32.client.Dispatch("Excel.Application")
COM Servers
class PythonUtilities:
_public_methods_ = [ 'SplitString' ]
_reg_progid_ = "PythonDemos.Itilities"
# Never copy the following ID
# use "print pythoncom.CreateGuid()" to make a new one
_reg_clsid_ = '{EFC3F30B-FB1B-40BE-8834-00F061BFAA6C}'
def SplitString(self, val, item=None):
import string
if item != None: item = str(item)
return string.split(str(val), item)
# Add code so that when this script is run by
# Python.exe, it self registers.
if __name__ == '__main__':
print "registering COM server...'
import win32com.server.register
win32com.server.register.UseCommandLine(PythonUtilities)
CORBA
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OmniORB, one of only 3 Corba 2.1 compliant ORBS
Wrapper classes are statically generated from IDL files, so you
get editor auto-completion on your remote objects :-)
CORBA Client
>>>import sys,CORBA,Snake
>>>orb =CORBA.ORB_init(sys.argv,CORBA.ORB_ID)
>>>adder =orb.string_to_object("corbaname:rir:#adder.obj")
>>>adder.accumulate(5)
5
>>>adder.accumulate(6)
11
>>>adder.accumulate(42)
53
>>>adder.reset()
>>>adder.accumulate(10)
10
CORBA Server
import sys,CORBA,CosNaming,Snake,Snake__POA
class Adder_i (Snake__POA.Adder):
def __init__(self):
self.value =0
def accumulate(self,a):
self.value =self.value +a
return self.value
def reset(self):
self.value =0
orb = CORBA.ORB_init(sys.argv,CORBA.ORB_ID)
poa = orb.resolve_initial_references("RootPOA")
adderServant = Adder_i()
poa.activate_object(adderServant)
adderObjref = adderServant._this()
nameRoot = orb.resolve_initial_references("NameService")
nameRoot = nameRoot._narrow(CosNaming.NamingContext)
name = [CosNaming.NameComponent("adder","obj")]
nameRoot.rebind(name,adderObjref)
poa._get_the_POAManager().activate()
orb.run()27
Java Integration
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Jython - Python running on JVM
http://www.jython.org/
http://www.jython.org/applets/index.html
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JPE - Java Python Bridge (Linking at JNI level)
http://jpe.sourceforge.net/
Delphi integration
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Complete set of Delphi components which wrap up Python
Part 5
Testing with Python
Testing Tools
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Interactive Prompt
Doctest
Unittest
Crosschecker
Interactive Prompt
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test functions as you write them
DocTest
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comment your code with docstrings showing interactive
prompt sessions
it replays them and checks the output is as specified
unittest
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same as JUnit and pals.
Aggregates tests.
Testing Approaches
Two approaches to testing:
• call your APIs to check they work
• use Python's glue capabilities to test systems end to end
Crosschecker
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Commercial product from Secret Labs with an IDE geared to
writing and running test cases.
Part 6
Conclusion
Conclusion
Python is the most cost-effective and general way to test systems in
other languages - at unit and end-to-end level.
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Python
http://www.python.org/
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ReportLab
http://www.reportlab.com/
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Jython
http://www.jython.org/
http://www.jython.org/applets/index.html
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JPE
http://jpe.sourceforge.net/
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Secret Labs
http://www.pythonware.com/