UppLYSning om Python

Vad är Python?

Nisch

Historik

Grunderna i Python

Python 1.3 (Oct 22 1995) [C]

Copyright 1991-1995 Stichting Mathematisch 
Centrum, Amsterdam

>>> 370*7*1.25

3237.5

>>> _+10*7*1.25

3325.0

>>> def USA_pris(x):

...   return x*7*1.25

... 

>>> USA_pris(370+10)

3325.0

Aritmetik

>>> 1+2

3

>>> 1+2.0

3.0

>>> 1+2L

3L

>>> pow(17,17L) 

827240261886336764177L

>>> -1/2

-1

>>> -1/2.0

-0.5

Tilldelningar

>>> x=y=z=7

>>> print x,y,z

7 7 7

>>> (x,y,z)=(2*3,3*4,4*5)

>>> print x,y,z

6 12 20

Relationer

>>> x<y<z

1

>>> x<>y and x!=y and not x==y

1

Strängar

>>> word = 'Help' + 'A'

>>> word

'HelpA'

>>> '<' + word*5 + '>'

'<HelpAHelpAHelpAHelpAHelpA>'

>>> print '"Isn\'t," she said.'

"Isn't," she said.

>>> "\"Isn't,\"" == '"Isn\'t,"'

1

>>> print "foo \n \' \" \\ bar \*"

foo 

 ' " \ bar \*

Strängar (forts.)

>>> word

'HelpA'

>>> word[4]

'A'

>>> word[0:2]

'He'

>>> word[2:4]

'lp'

>>> word[:2] 

'He'

>>> word[2:] 

'lpA'

>>> word[:2] + word[2:]

'HelpA'

Strängar (forts.)

>>> word[4]='a'

Traceback (innermost last):

  File "<stdin>", line 1, in ?

TypeError: can't assign to this subscripted 
object

>>> word[:1]+'a'+word[2:]

'HalpA'

>>> ord('a')

97

>>> chr(97)

'a'

Listor

>>> a = ['spam', 'eggs', 100, 1234]

>>> a

['spam', 'eggs', 100, 1234]

>>> a[0]

'spam'

>>> a[3]

1234

>>> a[-2]

100

>>> a[1:-1]

['eggs', 100]

>>> a[:2] + ['bacon', 2*2]

['spam', 'eggs', 'bacon', 4]

Listor (forts.)

>>> a

['spam', 'eggs', 100, 1234]

>>> a[2] = a[2] + 23

>>> a

['spam', 'eggs', 123, 1234]

>>> a[0:2] = [1, 12]

>>> a

[1, 12, 123, 1234]

>>> a[0:2] = []

>>> a

[123, 1234]

>>> a[1:1] = ['bletch', 'xyzzy']

>>> a

[123, 'bletch', 'xyzzy', 1234]

Listor (forts.)

>>> q = [2, 3]

>>> p = [1, q, 4]

>>> len(p)

3

>>> p[1]

[2, 3]

>>> p[1][0]

2

>>> p[1].append('xtra') 

>>> p

[1, [2, 3, 'xtra'], 4]

>>> q

[2, 3, 'xtra']

Kontrollstrukturer

>>> if x < 0:

...      x = 0

...      print 'Negative changed to zero'

... elif x == 0:

...      print 'Zero'

... elif x == 1:

...      print 'Single'

... else:

...      print 'More'

Kontrollstrukturer (forts.)

>>> # Measure some strings:

... a = ['cat', 'window', 'defenestrate']

>>> for x in a:

...     print x, len(x)

cat 3

window 6

defenestrate 12

>>> # Fibonacci series:

... # the sum of two elements defines the next

... (a, b) = (0, 1)

>>> while b < 10:

...       print b,

...       (a, b) = (b, a+b)

1 1 2 3 5 8

Kontrollstrukturer (forts.)

...     for x in range(2, n):

...         if n % x == 0:

...            print n, 'equals', x, '*', n/x

...            break

...     else:

...          print n, 'is a prime number'

Tupler

>>> t = 12345, 54321, 'hello!'

>>> t[0]

12345

>>> t

(12345, 54321, 'hello!')

>>> # Tuples may be nested:

... u = t, (1, 2, 3, 4, 5)

>>> u

((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))

>>> empty = ()

>>> singleton = ('hello',)

>>> x, y, z = t

Tabeller

>>> tel = {'jack': 4098, 'sape': 4139}

>>> tel['guido'] = 4127

>>> tel

{'sape': 4139, 'guido': 4127, 'jack': 4098}

>>> tel['jack']

4098

>>> del tel['sape']

>>> tel['irv'] = 4127

>>> tel

{'guido': 4127, 'irv': 4127, 'jack': 4098}

>>> tel.keys()

['guido', 'irv', 'jack']

>>> tel.has_key('guido')

1

Mer om jämförelser

(1, 2, 3)              < (1, 2, 4)

[1, 2, 3]              < [1, 2, 4]

'ABC' < 'C' < 'Pascal' < 'Python'

(1, 2, 3, 4)           < (1, 2, 4)

(1, 2)                 < (1, 2, -1)

(1, 2, 3)              = (1.0, 2.0, 3.0)

(1, 2, ('aa', 'ab')) < (1, 2, ('abc', 'a'), 4)

{'foo':0} < 2

{'bar':0} < {'foo':-1}

Moduler

    a, b = 0, 1

    while b < n:

          print b,

          a, b = b, a+b

def fib2(n): # return Fibonacci series up to n

    result = []

    a, b = 0, 1

    while b < n:

          result.append(b)

          a, b = b, a+b

    return result

Moduler (forts.)

>>> import fibo

>>> fibo.fib(1000)

1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987

>>> fibo.fib2(100)

[1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

>>> fibo.__name__

'fibo'

>>> fib = fibo.fib

>>> fib(500)

1 1 2 3 5 8 13 21 34 55 89 144 233 377

>>> from fibo import fib, fib2

>>> fib2(100)

[1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

Klasser och objekt

class ClassName:

                <statement-1>

                .

                .

                .

                <statement-N>

class MyClass:

                i = 12345

                def f(x):

                        return 'hello world'

>>> x=MyClass()

Klasser och objekt

# Function defined outside the class

        def f1(self, x, y):

                return min(x, x+y)

        class C:

                f = f1

                def g(self):

                        return 'hello world'

                h = g

class Bag:

                def empty(self):

                        self.data = []

                def add(self, x):

                        self.data.append(x)

                def addtwice(self, x):

                        self.add(x)

                        self.add(x)

>>> class Complex:

...     def __init__(self, realpart, imagpart):

...         self.r = realpart

...         self.i = imagpart

... 

>>> x = Complex(3.0,-4.5)

>>> x.r, x.i

(3.0, -4.5)

class DerivedClassName(BaseClassName1, BaseClassName2):

                <statement-1>

                .

                .

                .

                <statement-N>

Felhantering

>>> numbers = [0.3333, 2.5, 0, 10]

>>> for x in numbers:

...     print x,

...     try:

...         print 1.0 / x

...     except ZeroDivisionError:

...         print '*** has no inverse ***'

0.3333 3.00030003

2.5 0.4

0 *** has no inverse ***

10 0.1

Felhantering (forts.)

>>> def this_fails():

...     x = 1/0

>>> try:

...     this_fails()

... except ZeroDivisionError, d:

...     print 'Handling run-time error:', d

Handling run-time error: integer division or 
modulo

>>> raise NameError, 'HiThere'

Traceback (innermost last):

  File "<stdin>", line 1

NameError: HiThere

Felhantering (forts.)

>>> my_exc = 'my_exc'

>>> try:

...     raise my_exc, 2*2

... except my_exc, val:

...     print 'My exception occurred, value:', 
val

My exception occurred, value: 4

>>> try:

...     raise KeyboardInterrupt

... finally:

...     print 'Goodbye, world!'

... 

Standardmoduler

Allmänt

Strängar

Matematik

Operativsystem

UNIX-specifikt

Fönstersystem

Nuvarande implementation & verktyg