Python (& Jython) introduction - Benvenuti al sito di Alex Martelli

56 Pages·2003·0.37 MB·English

by  Alex Martelli

Python ( ) introduction
& Jython
for C++ and Java programmers
Alex Martelli <[email protected]>
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© 2003 AB Strakt April 3, 2003
Python is... ...:
lots of nice buzzwords
a Very-High-Level Language (VHLL)
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clean, spare syntax
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simple, regular, orthogonal semantics
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high-productivity
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open-source, cross-platform
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object-oriented
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...
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© 2003 AB Strakt -- A. Martelli April 3, 2003 1
Python is... ...:
a lot like Java
compiler to bytecode + VM/interpreter
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• however, compilation is implicit (“auto-make”)
everything (in 2.2) inherits from object
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consistent “object-reference” semantics
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• assignment, argument-passing, ...
• applies to numbers too (immutable, like strings)
large, powerful standard library
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introspection, serialization, threading...
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© 2003 AB Strakt -- A. Martelli April 3, 2003 2
Python is... ...:
a lot like C++
multi-paradigm
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• object-oriented, procedural, ...
multiple inheritance
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operator overloading
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signature-based polymorphism
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• as if “everything was a template”... w/ clean syntax
choices, choices everywhere
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• GUIs, Web server frameworks, COM/Corba/...
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© 2003 AB Strakt -- A. Martelli April 3, 2003 3
Python is... ...:
quite unlike either
strong but dynamic typing
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• objects have (strong) types, names don’t
• no declarations -- only statements
clean syntax, minimal “chart-junk”
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• blocks have no { } -- just indentation
• if/while have no ( )
most everything is a first-class object
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• including classes, functions, modules, packages...
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Python versions/releases
Classic Python: currently 2.2 -> 2.3
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• implemented in 1990-level ISO C
Jython: currently 2.1 -> (2.2/2.3)
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• implemented as 100% pure Java
• deploy just like Java, on a JVM
• transparently use/extend/implement arbitrary
Java classes and interfaces / compile to Java / ...
Others: experimental/research level
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• Python.NET , PyPy , Vyper (O’CAML), ...
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Python resources on the net
http:// www.python.org
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• just about everything: downloads, docs,
mailing lists, SIGs, pointers to [whatever], ...
• http://www.python.org/ftp/python/2.3/Python-2.3a2.exe
http://www.jython.org
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• mostly Jython-specific stuff
news:comp.lang.python
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• any kind of question, request, discussion
http://www.google.com
( )
no, really!!!
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© 2003 AB Strakt -- A. Martelli April 3, 2003 6
Python fundamentals
interactive interpreter (text and IDLE)
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• mostly for trying things out, or as a calculator
• prompts with >>>, shows expressions' results
program files (afile.py, afile.pyc, ...)
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• for most uses; compilation is automatic
assignment ( ):
simplest form
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• name = <any expression>
• creates name if needed, binds it to the value
• names are not declared, and have no type per se
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assignments, print
myvar = 'hello' # creates a name
myvar = 23 # rebinds name
question = answer = 42
myvar, answer = answer, myvar
print myvar, answer, question
42, 23, 42
if myvar<20: myvar = 10 # not executed
if myvar>40: myvar = 50 # executed
print myvar
50
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conditional statements
if question>30: # 'if' guards a suite
question = 20 # the suite is shown
x = 33 # by its indentation
else: # optional 'else'
x = 99 # indentation again
if x<30: myvar = 10 # not met
elif x<40: myvar = 20 # met
elif x<50: myvar = 40 # not evaluated
else: myvar = 40 # this neither
print x, question, myvar
33 20 20
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