Einführung in Python

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n = 10
# n wird integer
while n <= 13:
if n % 2 == 0:
print n, "gerade"
else:
print n, "ungerade"
n = n + 1
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Python 2.1.1 (#20, Jul 20, 2001)
>>> print 3*4
12
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#!/usr/bin/python
print 'Hello world!'
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/home/dirk/$ python test.py
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#include "Python.h"
Py_initialize;
PyRun_SimpleString("print 4");
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if, while, for, break, continue
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2323299094L
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$
'Python'
u"Hello\u0020world!"
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(3, 4.0)
['spam', 4, 1.0]
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{'egg':23, 'ham':40}
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s = 'eggs'
len(s)
s[0]
s[-1]
s[1]='a'
s = 'sliceofspam'
s[2:5]
s[:5]
s[-4:]
A+ /
#
#
#
#
=
4
(eingebaute Funktion)
'e'
's'
TypeError!
# 'ice'
# 'slice'
# 'spam'
'a' * 99999
# 'aaaaaaaaaaaaaaaaa...'
"eggs".capitalize()
# 'EGGS'
"The %s who say %s' % ('knights', 'Ni!')
'Neue Zeile\n'
# \n ist Newline
B+
B+
A+ /
t = (0, "python", 1.5)
t[1]
t[1:3]
# heterogen
# 'python'
# ('python', 1.5)
v = (3, (1,2,3), 7)
v[1]
# verschachtelbar
# (1,2,3)
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a, b, c = 4, "Python", -1.0
x, y = y, x
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# tauscht Werte
%
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L = ['spam', 3.14, 42]
L[1] = 'eggs'
L[0:2] = [4,3,2,1]
# ['spam', 'eggs', 42]
# [4,3,2,1,42]
L.sort()
L.append('a')
L.pop()
# [1,2,3,4,42]
# [1,2,3,4,42,'a']
# 'a' (Liste als Stack)
42 in L
range(4)
# 1
(true)
# [0,1,2,3]
[x*x for x in [1,2,3,4] if x * x > 6]
# [9, 16]
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dict = {'schmitz': 5325, 'meier': 2345,
'huber': 'kein Telefon'}
dict['schmitz']
# 5325
dict.keys()
# ['meier','schmitz','huber']
dict.values()
# [2345, 5325, 'kein Telefon']
dict.has_key('meier')
# 1
(true)
dict['mueller'] = 9876
# neu einfügen
del dict['mueller']
# wieder entfernen
for key in dict.keys():
print key, "--", dict[key]
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myfile = open('text.txt', 'r')
s = myfile.readlines()
print "Anzahl Zeilen:", len(s)
myfile.close()
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myfile.read()
myfile.read(n)
myfile.readline()
myfile.seek(pos)
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myfile = sys.stdin
myfile = sys.stdout
# zum Lesen öffnen
# Liste von Zeilen
# Schließen (optional)
2/6)
#
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#
#
in einen String einlesen
n Bytes einlesen
nächste Zeile
Zugriff über Position
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try:
myfile = open('text.txt','r')
except IOError, data:
print 'Oeffnen nicht moeglich: ', data
else:
print 'Alles ok.'
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myException = 'Fehler'
...
if notOK: raise myException
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# String als Exception
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try:
doSomething()
finally:
# fängt Exception nicht ab
print "wird immer ausgeführt"
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if __debug__:
if not test:
raise AssertionError, data
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def factorial(n):
"Fakultaet von n"
# optionaler Doc-String
result = 1L
# Long Integer
while n > 1:
result = result * n
n = n - 1
return result
# optional, sonst 'None'
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def factorial(n=10)
def factorial(n,*others)
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id(obj)
type(obj)
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id("Python")
type("Python")
id(5+4)
type(5+4)
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135181080
<type 'string'>
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<type 'int'>
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a = 42
id(a)
type(a)
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# 135139460
# <type 'int'>
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b = a
id(b)
b is a
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# 135139460
# 1 (true)
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a = [1,4,5]
a = a[2]
def a(n):return n
type(a)
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a weist auf Liste
a weist auf Element der Liste
a weist auf Funktion
<type 'function'>
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a = [1, 2]
b = a
b[0] = [5]
print b
print a
# erstes Element der Liste ändern
# [[5], 2]
# [[5], 2]
a = [1,2]
b = a
b = [5]
print b
print a
# neues Objekt [5] an b binden
# [5]
# [1, 2]
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#
g
a
b
46
globaler Geltungsbereich
= 1
= 3
= 15
def func(x):
# lokaler Geltungsbereich
global g
g = b + 1
a = x * 2
return a
print
print
print
print
print
print
func(15)
a
g
b
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func
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3
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NameError: name 'x' not defined
<function 'func' at 009970C>
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x = 2.0
def outer():
x = 2.2
def inner()
print x
inner()
outer()
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# 2.0
(in v2.0)
# 2.2
(in v2.2)
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import math
print math.pi
# importiert den Namen 'math'
# 3.1415926535926535
from math import exp
exp(1)
# import math; exp = math.exp
# 2.7182818284590451
from math import *
# alle Namen
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reload()
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class Counter:
def __init__(self):
# Konstruktor
self.value = 0
# Attribut der Instanz
def inc(self, n):
# Methode
self.value = self.value + n
c = Counter()
print c.value
c.inc(3)
Counter.inc(c, 3)
print c.value
c.value = 7
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Instanz erzeugen
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Alternativschreibweise
6
Attribute sind public
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class Derived(Counter):
def inc(self, n = 1):
Counter.inc(self, n)
def dec(self, n = 1):
self.value -= n
def __repr__(self):
print 'Zaehlerstand =',
# Operator overloading
self.value
d = Derived()
d.inc()
print d
# 'Zaehlerstand = 1'
# Methode überschreiben
# kein 'super'
# Klasse erweitern
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self.value
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class MyClass(A, B)
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