Datatypes

i = 666

type(i)

int

Strings Intro

ein_string = 'hallo'
ein_string

'hallo'

print(ein_string)

hallo

ein_anderer_string = "hallo"

print(ein_anderer_string)

hallo

s = 'ein paar zeichen, gefolgt von "double quotes", dann noch was'

s = "abc ' fghjgfgh' "

s

"abc ' fghjgfgh' "

s = '"" \'dfghgfgh '

s

'"" \'dfghgfgh '

for i in [1,2,3]:
    print(i)
    print(i+1)
print('vorbei')

1
2
2
3
3
4
vorbei

Doc Strings

def do_something(a, b):
    '''diese funktion ist komplett sinnlos, und nimmt parameter a und b, die integers
    sein sollten, sonst funktioniert das ganze hier nicht.

    der returnwert ist noch sinnloserer weise die summe der parameter.'''

    # hier wird die komplexe berechnung der summe vorgenommen. obacht!
    return a + b

x = do_something(1, 2)
x

3

type(do_something)

function

do_something.__doc__

'diese funktion ist komplett sinnlos, und nimmt parameter a und b, die integers\n    sein sollten, sonst funktioniert das ganze hier nicht.\n    \n    der returnwert ist noch sinnloserer weise die summe der parameter.'

help(do_something)

Help on function do_something in module __main__:

do_something(a, b)
    diese funktion ist komplett sinnlos, und nimmt parameter a und b, die integers
    sein sollten, sonst funktioniert das ganze hier nicht.

    der returnwert ist noch sinnloserer weise die summe der parameter.

Variablen

try:
    print(nix)
except Exception as e:
    print(e, type(e))

name 'nix' is not defined <class 'NameError'>

nix = 666
print(nix)

666

Object Identity

a = 42
id(a)

140672599989840

b = a
id(b)

140672599989840

b = [1,2,3]

id(b)

140672464974720

Integers

Hoechste Integer Zahl auf 64 Bit Rechnern:

num = 2**64 -1
num

18446744073709551615

num = num +1

num

18446744073709551616

num = 2**64

num

18446744073709551616

2**100000

99900209301438450794403276433003359098042913905418169177152927386314583246425734832748733133244965040316439444555585493001879966076561765629084713542474928751988896298736710932463504273731124792658002785312410887370856052872283901645686910268506759235179146970528576446968015248323454755432502927865208069577709717411022320429763512053307779968979251166198707717857759555217200813202952046179492292592956239209657978735581586675254957973131448062492602618379413050805826860315351341787396228349908863577580621046066363721305877953223449720108084863695414018358513598580356035740218729081555665806071864612689728397946218422675793496388933572475887619591376567624111250207087048704651793963987101092003639347456180906016133778985602968635985580247614489330470522228601313770959583573194858984964045723838751707022423326334368944232973818777331532869442179361253019078689036036632831615027261399341528040711719149239033418749353944558963012921972564177172335435447515523793108922681824024527557520947046421859438628656327442313320847422215514933150027177500642288262118225493496005574573349646784832691809518959557691745096732244177404328404558821091379053756467721399766217852650571698548345624875183223832503186455054721143699341679816781702551228129780651948062954053391546574799412974991903485075443364145056316573960066933824273164340395801212802609842122475142078347122248314103040686037196401618557416564394722534649452497003145098900931622689527444287054764254722531675145211822314553883743082326422006330251375331293651643417252062561553117947386191429047614456549271284181751835313270529754953705614382395732279396730301060774568484774278321953492279838364361637647429695459066723691241363259321233356431358944652191018821238297409079163860232354509593887667364032295779939011521544480036372150691155911119960015305891077294210322304242620356934932160529275696258584458223545946452769231081973058062803265167364493437617324097533423332897302829591735692730132864233117596052304951716770331637095222569524604021433876551976440165281480223483318810975594219604764793885201985410173489859485110054692466172341431353099384059232689535865388869744270086070286355020855620295493524800507965215649196832651067441009678229519541616177175429975200098873073778762106858907709694116104380286239504453237895918707602892603934898261007748876728529181064684891438936490647845912116121933007079005370590421880128565594036990708880329668716116559612323319983109232250828661803218804394475729867620969358197843859279692501233269351946932077243355273655662482237878338880749992768316334403186044636187037897843130328438234704109443065914719283411909751852392123276743849905615636884329390394420026175309768506051329371014490863961416205560535473355699267009413752718291424072342679375650697655674759341013102253428300804090795873295442135513073020501715984242307604692097329072901416063539608805592023573768856478522400927771114891344924169956071717862984365339781808694741067511113535237115404365993108896974856588008878619749343579292462040517672460122506184040119662898726738030704983612179744846791007478463561946648292247361341151355671792917819680560537264841411283478582412591219546011844124093497829633170420025304186616949623187358606524854102222118695442237882891897120805145751413619648053697231645705649984795376571745481285974060773391587753323552156094359192751993510142222469630170137174193375049192953632951011152929518362828191918216516764559465158280489842561167481503678052678786627169996492969493770457948761466281109299820207370133303244510053853785511888034741481986651145793226849009930002367361685552941734420599253719652449979254831593437063439703718096114703230741869850350547222890271748503333683283002811329108416931504573899331839345932929949427960153097561187089189295284490742432847670062431711716227317666067961019678022045645890158995247047410011581109636337313293883568689494087593341769093878063985846473005889281759988444774861300631530687600700848372675277897773568300427789027721056838330214702797285953363321105640642639097245799496861629080196041417539357688765879924285499121517379242703432486484142474568388895418932414509875057594030132496975416969553302968802193048741635010979200362102387682751763699809776149796360967043481401241306835768799049974365962964957054595247353820003637703248949821033313329135623151698544104153170541939282347233988484535521732036880883121009439414349382822035496502815307510870986046812248029738256312449893319652962023726085865090503079933086520012316719151827657420956895131361840954121214737863110428977178614481583169658487669495548262525049612270447147122296202746823629098038774693769873589421254417923552983874798304502539097887334697326030975441564748054737327327672486527590349953363541269539004588549886835749278646152520408004901147858922890854433539969947808674716135197858385714564215831711930041179894407902683463575503398880867251278835772976264992138274365739929273022387925769242327854872012972553860719683037824830637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8131048296612979081477663269791394570357390537422769779633811568396223208402597025155304734389883109376

0b100110

38

1 == 2

False

1 < 2

True

1 + (2 * 3)

7

(1 + 2) * 3

9

2 * 3 * 4

24

20 % 3

2

2 * 10 % 3

2

(2 * 10) % 3

2

Exponentiation

2**64

18446744073709551616

3 * 2**64 == 3 * (2**64)

True

Floor Division

3 / 2    # <----------------- Python 3!!!!!

1.5

3//2

1

Variablen? Datenypen?

type(do_something)

function

type(a)

int

a = do_something

type(a)

function

help(a)

Help on function do_something in module __main__:

do_something(a, b)
    diese funktion ist komplett sinnlos, und nimmt parameter a und b, die integers
    sein sollten, sonst funktioniert das ganze hier nicht.

    der returnwert ist noch sinnloserer weise die summe der parameter.

a(2, 3)

5

a.__doc__

'diese funktion ist komplett sinnlos, und nimmt parameter a und b, die integers\n    sein sollten, sonst funktioniert das ganze hier nicht.\n    \n    der returnwert ist noch sinnloserer weise die summe der parameter.'

dir(a)

['__annotations__',
 '__call__',
 '__class__',
 '__closure__',
 '__code__',
 '__defaults__',
 '__delattr__',
 '__dict__',
 '__dir__',
 '__doc__',
 '__eq__',
 '__format__',
 '__ge__',
 '__get__',
 '__getattribute__',
 '__globals__',
 '__gt__',
 '__hash__',
 '__init__',
 '__init_subclass__',
 '__kwdefaults__',
 '__le__',
 '__lt__',
 '__module__',
 '__name__',
 '__ne__',
 '__new__',
 '__qualname__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__']

a.__name__

'do_something'

a.__class__

function

Objects, Classes

class Karteikarte:
    def __init__(self, firstname, lastname, svnr):
        self.firstname = firstname
        self.lastname = lastname
        self.svnr = svnr
    def format(self):
        my_formatted_person = self.firstname + ' ' + self.lastname + ' (' + self.svnr + ')'
        return my_formatted_person

joerg = Karteikarte('Joerg', 'Faschingbauer', '1037190666')
caro = Karteikarte('Caro', 'Faschingbauer', '123425041997')

print(joerg.firstname + ' ' + joerg.lastname + ' (' + joerg.svnr + ')')

Joerg Faschingbauer (1037190666)

print(caro.firstname + ' ' + caro.lastname + ' (' + caro.svnr + ')')

Caro Faschingbauer (123425041997)

caros_string = caro.format()
joergs_string = joerg.format()

print(caros_string)

Caro Faschingbauer (123425041997)

dir(caro)

['__class__',
 '__delattr__',
 '__dict__',
 '__dir__',
 '__doc__',
 '__eq__',
 '__format__',
 '__ge__',
 '__getattribute__',
 '__gt__',
 '__hash__',
 '__init__',
 '__init_subclass__',
 '__le__',
 '__lt__',
 '__module__',
 '__ne__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 '__weakref__',
 'firstname',
 'format',
 'lastname',
 'svnr']

caro.__class__

__main__.Karteikarte

caro.format

<bound method Karteikarte.format of <__main__.Karteikarte object at 0x7ff0dc48b490>>

und strings???

s = 'Mississippi'

s.__class__

str

type(s)

str

s.count('ss')

2

pos = s.find('ss')

pos

2

next_pos = s.find('ss', pos+1)

next_pos

5

Datatype Conversions

type(str)

type

type(Karteikarte)

type

s = str('abc')

s

'abc'

s = 'abc'

s

'abc'

i = 42

s = str(i)
s

'42'

type(int)

type

i = int('666')

i

666

type(i)

int

int('0xdeadbeef', 16)

3735928559

float('0.1234')

0.1234

try:
    float('Joerg')
except Exception as e:
    print(e, type(e))

could not convert string to float: 'Joerg' <class 'ValueError'>

bool(1)

True

bool(42)

True

bool(-1)

True

bool(0)

False

bool('Joerg')

True

bool('')

False

if 'Joerg':
    print('Oida!')

Oida!

if len('Joerg') != 0:
    print('Oida!')

Oida!

l = [1,2,3]
type(l)

list

l = list('Joerg')
l

['J', 'o', 'e', 'r', 'g']

import this

The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!

Boolean

True and False

False

True or False

True

False or False

False

True and True

True

False and True

False

def wahr():
    print('wahr')
    return True
def falsch():
    print('falsch')
    return False

x = wahr()
print(x)

wahr
True

if wahr():
    print('jo eh')
else:
    print('nix da')

wahr
jo eh

if wahr() and wahr():
    print('jo eh')

wahr
wahr
jo eh

if wahr() or falsch():
    print('jo eh')

wahr
jo eh

if falsch() and wahr():    # False and True
    print('jo eh')
else:
    print('nix da')

falsch
nix da

Compound Datatypes

Listen

l = [1, 2, 'drei', ['4.0', 5], 666.7]

len(l)

5

l[0]

1

l[3]

['4.0', 5]

l[3][1]

5

l[2][2]

'e'

l[3][0][1]

'.'

try:
    l[4][3]
except Exception as e:
    print(e, type(e))

'float' object is not subscriptable <class 'TypeError'>

BTW, wie kriegt man die Nachkommastellen aus einem Float raus?

f = 666.789

Erste Moeglichkeit:

round((f - (int(f))) * 1000)

789

Zweite Moeglichkeit:

f_str = str(f)
f_str

'666.789'

punkt_pos = f_str.find('.')

punkt_pos

3

nachkomma_str = f_str[punkt_pos+1:]

int(nachkomma_str)

789

Weiter im Text …

l

[1, 2, 'drei', ['4.0', 5], 666.7]

l.append('sieben')

l

[1, 2, 'drei', ['4.0', 5], 666.7, 'sieben']

l.extend(['eight', 9.0])

l

[1, 2, 'drei', ['4.0', 5], 666.7, 'sieben', 'eight', 9.0]

l.extend('aber hallo')

l

[1,
 2,
 'drei',
 ['4.0', 5],
 666.7,
 'sieben',
 'eight',
 9.0,
 'a',
 'b',
 'e',
 'r',
 ' ',
 'h',
 'a',
 'l',
 'l',
 'o']

l1 = [1,2,3]
l2 = ['vier', 'fuenf']
l = l1+l2
l

[1, 2, 3, 'vier', 'fuenf']

Tuple

t = (1,2,3)

t[0]

1

t[1:]

(2, 3)

try:
    t.append(4)
except Exception as e:
    print(e, type(e))

'tuple' object has no attribute 'append' <class 'AttributeError'>

Single element tuples?

t = (1)     # '(', ')': Operator praezedenz
type(t)

int

(1+2)*3

9

t = ((1))
t

1

[(1)]

[1]

(1,)

(1,)

t1 = (1,2,3)
t2 = ('vier', 'fuenf')
t = t1+t2
t

(1, 2, 3, 'vier', 'fuenf')

Dictionary

table = {'one': 1,
        'two': 2}

table['two']

2

table['three'] = 3

'three' in table

True

'four' in table

False

del table['one']

'one' in table

False

'one' not in table

True

not 'one' in table

True

Set

Sequentielle Suche in Liste

l = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

2 in l

True

11 in l

True

12 in l

False

s = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}

11 in s

True

s.remove(11)

11 not in s

True

type(s)

set

Frage: wie wandele ich ein Dictionary in ein Set um? Oder gach in eine Liste?

table

{'two': 2, 'three': 3}

list('Joerg')   # <-- ITERATION

['J', 'o', 'e', 'r', 'g']

set('Joerg')

{'J', 'e', 'g', 'o', 'r'}

for k in table.keys():
    print(k)

two
three

for k in table:
    print(k)

two
three

set(table)

{'three', 'two'}

Wie mache ich aus einem Set ein Dictionary? (Hm. Woher kommen die Keys?)

import random

s = {1, 2, 3}

d = {}
for element in s:
    d[element] = random.randrange(100)

d

{1: 65, 2: 45, 3: 69}

Python Standard Libarary Examples

collections

ChainMap

from collections import ChainMap

d1 = {'one': 1, 'two': 2}
d2 = {'three': 3, 'four': 4}

chained = ChainMap(d1, d2)
chained['one']

1

chained['three']

3

chained['five'] = 5

d1

{'one': 1, 'two': 2, 'five': 5}

d2

{'three': 3, 'four': 4}

try:
    d['ten']
except Exception as e:
    print(e, type(e))

'ten' <class 'KeyError'>

deque

Liste vorne anhaengen:

l = [3,4,5]
l.append(6)

l.insert(0, 2)
l

[2, 3, 4, 5, 6]

del l[0]

l

[3, 4, 5, 6]

Aber: langsamer als man sich wuenschen wuerde

import collections

d = collections.deque([3, 4, 5])

d

deque([3, 4, 5])

d.append(6)
d

deque([3, 4, 5, 6])

d.appendleft(2)
d

deque([2, 3, 4, 5, 6])

d.extend('Joerg')
d

deque([2, 3, 4, 5, 6, 'J', 'o', 'e', 'r', 'g'])

d.extendleft('Faschingbauer')
d

deque(['r',
       'e',
       'u',
       'a',
       'b',
       'g',
       'n',
       'i',
       'h',
       'c',
       's',
       'a',
       'F',
       2,
       3,
       4,
       5,
       6,
       'J',
       'o',
       'e',
       'r',
       'g'])

relem = d.pop()
relem

'g'

d

deque(['r',
       'e',
       'u',
       'a',
       'b',
       'g',
       'n',
       'i',
       'h',
       'c',
       's',
       'a',
       'F',
       2,
       3,
       4,
       5,
       6,
       'J',
       'o',
       'e',
       'r'])

d.popleft()

'r'

d

deque(['e',
       'u',
       'a',
       'b',
       'g',
       'n',
       'i',
       'h',
       'c',
       's',
       'a',
       'F',
       2,
       3,
       4,
       5,
       6,
       'J',
       'o',
       'e',
       'r'])

os.path

import os.path

os.path.join('a', 'b')

'a/b'

os.path.normpath('a/b/c/d/../../x')

'a/b/x'

Suchalgorithmen und Datenstrukturen (Ausflug)

l = [5, 3, 1, 10, 8, 0]
l.sort()

l

[0, 1, 3, 5, 8, 10]

l = [5, 3, 1, 10, 8, 0]
sorted_l = sorted(l)

l

[5, 3, 1, 10, 8, 0]

sorted_l

[0, 1, 3, 5, 8, 10]

t = (5, 3, 1, 10, 8, 0)
sorted_t = sorted(t)

t

(5, 3, 1, 10, 8, 0)

sorted_t

[0, 1, 3, 5, 8, 10]

type(sorted_t)

list

s = 'Joerg'
sorted_s = sorted(s)

s

'Joerg'

sorted_s

['J', 'e', 'g', 'o', 'r']

Slicing

text = 'Hello World'

len(text)

11

text[0:5]

'Hello'

text[:5]

'Hello'

text[6:11]

'World'

text[6:]

'World'

text = 'Mississippi'
pos = text.find('ss')
pos

2

subtext = text[pos:]
subtext

'ssissippi'

Copy:

text

'Mississippi'

id(text)

140672464726576

copied_text = text[:]
copied_text

'Mississippi'

id(copied_text)

140672464726576

l = [1,2,3]
copied_l = l[:]
copied_l

[1, 2, 3]

id(l)

140672464784832

id(copied_l)

140672464784064

Slice Assignment

l = [2, 3, 'a', 'b', 7]    # wanted: [2,3,4,5,6,7]

l[2:4]

['a', 'b']

l[2:4] = [4,5,6]
l

[2, 3, 4, 5, 6, 7]

l[:0]

[]

l[:0] = [0,1]
l

[0, 1, 2, 3, 4, 5, 6, 7]

l.insert(0, -1)
l

[-1, 0, 1, 2, 3, 4, 5, 6, 7]

l[len(l):]

[]

l[len(l):] = [8,9]

l

[-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Lesbarer:

l.extend([10,11])

l

[-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

References, (Im)mutability

a = 42

id(a)

140672599989840

b = a
id(b)

140672599989840

a += 1

a

43

id(a)

140672599989872

id(b)

140672599989840

b

42

Lists are mutable

l1 = [1, ['abc', 'def'], 3]
len(l1)

3

l1[0]

1

l1[1]

['abc', 'def']

l1[2]

3

Machen wir eine Kopie:

l2 = l1[:]

id(l1)

140672464751872

id(l2)

140672464768512

l1

[1, ['abc', 'def'], 3]

l2

[1, ['abc', 'def'], 3]

l1.append(4)
l1

[1, ['abc', 'def'], 3, 4]

l2

[1, ['abc', 'def'], 3]

l1[1]

['abc', 'def']

l2[1]

['abc', 'def']

l1[1].append('ghi')
l1

[1, ['abc', 'def', 'ghi'], 3, 4]

l2

[1, ['abc', 'def', 'ghi'], 3]

id(l1[1])

140672464594880

id(l2[1])

140672464594880

l1[1] is l2[1]

True

ist das gleiche wie …

id(l1[1]) == id(l2[1])

True

l1.insert(0, -100)
l1

[-100, 1, ['abc', 'def', 'ghi'], 3, 4]

l1[2] is l2[1]

True

l2

[1, ['abc', 'def', 'ghi'], 3]

l2[1].append('jkl')

l2

[1, ['abc', 'def', 'ghi', 'jkl'], 3]

l1

[-100, 1, ['abc', 'def', 'ghi', 'jkl'], 3, 4]

Shallow copy and deep copy

l1 = [1, ['abc', 'def'], 3]

Shallow copy:

l2 = l1[:]

l1[1] is l2[1]

True

Deep copy:

import copy

l3 = copy.deepcopy(l1)
l1[1] is l3[1]

False

l1[1].append('ghi')
l1

[1, ['abc', 'def', 'ghi'], 3]

l3

[1, ['abc', 'def'], 3]

while Loops

i = 0
while i < 10:
    i += 1
print(i)

10

i = 0
while i < 10:
    print('hallo suesser')
    i += 1

hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser

for i in range(10):
    print('hallo suesser')

hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser
hallo suesser

import random
while True:
    number = random.randrange(1,7)
    if number == 6:
        print('yay!')
        break
    else:
        print(f'lose ({number})')

lose (3)
lose (1)
lose (1)
lose (1)
lose (2)
lose (3)
yay!

else

Potschert: Flag

import random

sechser_gewuerfelt = False
n_tries = 0
while n_tries < 6:
    n_tries += 1
    number = random.randrange(1,7)
    if number == 6:
        sechser_gewuerfelt = True
        break

if sechser_gewuerfelt:
    print('yay!')
else:
    print('versager!')

yay!

import random

n_tries = 0
while n_tries < 6:
    n_tries += 1
    number = random.randrange(1,7)
    if number == 6:
        print('yay!')
        break
else:
    print('versager!')

versager!

for Loops, range()

for name in ['Caro', 'Johanna', 'Eva', 'Jörg']:
    print(name)

Caro
Johanna
Eva
Jörg

for _ in [0,1,2,3,4,5]:
    number = random.randrange(1,7)
    if number == 6:
        print('yay!')
        break
else:
    print('versager!')

versager!

for _ in range(6):     # python2: xrange()
    number = random.randrange(1,7)
    if number == 6:
        print('yay!')
        break
else:
    print('versager!')

yay!

for i in range(3):
    print(i)

0
1
2

for i in range(3,10):
    print(i)

3
4
5
6
7
8
9

for i in range(3,10,2):
    print(i)

3
5
7
9

Iterator Protocol

r = range(3)
r

range(0, 3)

type(r)

range

it = iter(r)
it

<range_iterator at 0x7ff0dc48bed0>

next(it)

0

next(it)

1

next(it)

2

try:
    next(it)
except StopIteration as e:
    print(e, type(e))

 <class 'StopIteration'>

for i in range(3):
    print(i)

0
1
2

Iteration over Compound Datatypes

s = {1,2,3}
for element in s:
    print(element)

1
2
3

d = {
    0: 'zero',
    1: 'one',
    2: 'two',
}

for element in d:
    print(element)

0
1
2

for key in d.keys():
    print(key)

0
1
2

for value in d.values():
    print(value)

zero
one
two

for element in d.items():
    print(element)

(0, 'zero')
(1, 'one')
(2, 'two')

for pair in d.items():
    key = pair[0]
    value = pair[1]
    print(f'Key: {key}, value: {value}')

Key: 0, value: zero
Key: 1, value: one
Key: 2, value: two

Tuple unpacking:

a, b = 1, 2

(a, b) = (1, 2)

a

1

b

2

t = (1, 2)
a, b = t

a

1

b

2

for key, value in d.items():
    print(f'Key: {key}, value: {value}')

Key: 0, value: zero
Key: 1, value: one
Key: 2, value: two

Functions

def maximum(a, b):
    if a < b:
        return b
    return a

maximum(1,2)

2

maximum('abc', 'def')

'def'

'abc' < 'def'

True

'Huber' > 'Hannes'

True

1 < 2

True

try:
    1 < 'abc'
except Exception as e:
    print(e, type(e))

'<' not supported between instances of 'int' and 'str' <class 'TypeError'>

try:
    maximum(1, 'abc')
except Exception as e:
    print(e, type(e))

'<' not supported between instances of 'int' and 'str' <class 'TypeError'>

[3,1,4] < [3,4,5]

True

maximum([3,1,4], [3,4,5])

[3, 4, 5]

Default Parameters

def greet(name, phrase):
    return phrase + ', ' + name
print(greet('Joerg', 'Hallo'))

Hallo, Joerg

def greet(name, phrase='Hallo'):
    return phrase + ', ' + name
greet('Joerg')

'Hallo, Joerg'

greet('Joerg', 'Gruess Gott')

'Gruess Gott, Joerg'

Default Parameters: Pitfalls

def fill_in_user(svnr, firstname, lastname, database):
    if database.get(svnr):
        raise Exception(svnr + ' gibts scho')
    database[svnr] = (firstname, lastname)

my_db = {}
fill_in_user('1037190666', 'Joerg', 'Faschingbauer', my_db)
my_db

{'1037190666': ('Joerg', 'Faschingbauer')}

def fill_in_user(svnr, firstname, lastname, database={}):
    if database.get(svnr):
        raise Exception(svnr + ' gibts scho')
    database[svnr] = (firstname, lastname)

fill_in_user('1037190666', 'Joerg', 'Faschingbauer')

try:
    fill_in_user('1037190666', 'Joerg', 'Faschingbauer')
except Exception as e:
    print(e, type(e))

1037190666 gibts scho <class 'Exception'>

dict.fromkeys()

dict.fromkeys(range(5))

{0: None, 1: None, 2: None, 3: None, 4: None}

dict.fromkeys(range(5), 666)

{0: 666, 1: 666, 2: 666, 3: 666, 4: 666}

l = [2, 3, 1, 10, 3, 3, 1, 10, 5, 2]
uniq_dict = dict.fromkeys(l)
uniq_dict

{2: None, 3: None, 1: None, 10: None, 5: None}

for key in uniq_dict.keys():
    print(key)

2
3
1
10
5

list(uniq_dict.keys())

[2, 3, 1, 10, 5]

Generators

Generator, der die Quadratzahlen startend von einem konfigurierbaren Startwert ausgibt …

Start = 3 9, 16, 25, 36, 49, …

def squares(start, max):
    l = []
    i = start
    while True:
        sqnum = i**2
        i += 1
        if sqnum == max:
            break
        l.append(sqnum)
    return l

for num in squares(3, 100):
    print(num)

9
16
25
36
49
64
81

def squares(start, max):
    i = start
    while True:
        sqnum = i**2
        i += 1
        if sqnum >= max:
            break
        yield sqnum

for num in squares(3, 100):
    print(num)

9
16
25
36
49
64
81

sq = squares(3, 50)
sq

<generator object squares at 0x7ff014b01820>

it = iter(sq)
next(it)

9

next(it)

16

next(it)

25

next(it)

36

next(it)

49

try:
    next(it)
except Exception as e:
    print(e, type(e))

 <class 'StopIteration'>

Miscellaneous String Methods

s = '    \n\r\t   '
s.isspace()

True

'abcDEF'.isalpha()

True

'abc'.isidentifier()

True

'_'.isidentifier()

True

'666'.isidentifier()

False

'abc'.capitalize()

'Abc'

'abc'.upper()

'ABC'

'hallo'.center(50)

'                      hallo                       '

'file.xslx'.endswith('.xslx')

True

s = 'mississippi'

s.find('ss')

2

s.find('ss', 3)

5

s.find('xxx')

-1

s.index('ss')

2

s.index('ss', 3)

5

try:
    s.index('xxx')
except Exception as e:
    print(e, type(e))

substring not found <class 'ValueError'>

join, split

l = ['abc', 'def']
','.join(l)

'abc,def'

import os.path

os.path.join('abc', 'def')

'abc/def'

'abc:def'.split(':')

['abc', 'def']

firstname, lastname = 'joerg:faschingbauer'.split(':')

firstname

'joerg'

lastname

'faschingbauer'

strip, lstrip, rstrip

'         abc       '.strip()

'abc'

'         abc       '.lstrip()

'abc       '

'         abc       '.rstrip()

'         abc'

'xy   abc    yz'.strip('xyz')

'   abc    '

List Comprehension

def squares(l):
    lret = []
    for i in l:
        lret.append(i**2)
    return lret

numbers = [1,2,3,4]
sqnums = squares(numbers)
for i in sqnums:
    print(i)

1
4
9
16

sqnums = [i**2 for i in numbers]
for i in sqnums:
    print(i)

1
4
9
16

for i in [i**2 for i in numbers if i%2 == 0]:
    print(i)

4
16

Raw Strings

s = 'C:\irgendwas\nochwas'

print(s)

C:\irgendwas
ochwas

s = 'C:\\irgendwas\\nochwas'

print(s)

C:\irgendwas\nochwas

s = r'C:\irgendwas\nochwas'

print(s)

C:\irgendwas\nochwas