Python Basics (2023-06-20 - 2023-06-22)

a = 1
b = 2

print(a)

1

print(b)

2

c, d = 3, 4

t = (3, 4)
type(t)

tuple

t = (3, 4, 5)

type(t)

tuple

tmp = c
c = d
d = tmp

c, d

(4, 3)

c, d = d, c

a = 42

id(a)

140640823526928

hex(id(a))

'0x7fe97e53c610'

b = a

id(b)

140640823526928

a += 1

id(a)

140640823526960

del b

try:
    b
except NameError as e:
    print('NameError(specific)')
except Exception as e:
    print(e, type(e))

NameError(specific)

b = None

type(b)

NoneType

print(b)

None

DataTypes

Integers

i = 2**64-1

hex(i)

'0xffffffffffffffff'

i += 1

i

18446744073709551616

hex(i)

'0x10000000000000000'

2**1000

10715086071862673209484250490600018105614048117055336074437503883703510511249361224931983788156958581275946729175531468251871452856923140435984577574698574803934567774824230985421074605062371141877954182153046474983581941267398767559165543946077062914571196477686542167660429831652624386837205668069376

Datatype Conversions

s = '666'
int(s)

666

int('0xdeadbeef', 16)

3735928559

int('666', 7)

342

str(666)

'666'

float(666)

666.0

float('42.666')

42.666

(Im)mutable?

l = [1, 2, 3]

id(l)

140640741310912

l.append(4)

l

[1, 2, 3, 4]

id(l)

140640741310912

t = (1,2,3)

id(t)

140640741034048

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

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

Compound Datatypes

List

l = [1, 2, 3, 'vier']

id(l)

140640741341184

l

[1, 2, 3, 'vier']

l.append(5.0)

l

[1, 2, 3, 'vier', 5.0]

len(l)

5

l.extend([6, 7, 'acht'])

l

[1, 2, 3, 'vier', 5.0, 6, 7, 'acht']

l.append([9, 10])

l

[1, 2, 3, 'vier', 5.0, 6, 7, 'acht', [9, 10]]

del l[8]

l

[1, 2, 3, 'vier', 5.0, 6, 7, 'acht']

for elem in l:
    print(type(elem))

<class 'int'>
<class 'int'>
<class 'int'>
<class 'str'>
<class 'float'>
<class 'int'>
<class 'int'>
<class 'str'>

[type(elem) for elem in l]

[int, int, int, str, float, int, int, str]

[elem for elem in l if type(elem) is not list]

[1, 2, 3, 'vier', 5.0, 6, 7, 'acht']

for e in l:
    print(e)

1
2
3
vier
5.0
6
7
acht

l += [9,10]

id(l)

140640741341184

l

[1, 2, 3, 'vier', 5.0, 6, 7, 'acht', 9, 10]

1 in l

True

2 in l

True

10 in l

True

666 in l

False

Dictionary

d = {'one': 1, 'two': 2, 3: 'three'}

d['one']

1

d[3]

'three'

len(d)

3

del d[3]

try:
    del d[2]
except Exception as e:
    print(e, type(e))

2 <class 'KeyError'>

d['three'] = 3

'three' in d

True

'four' in d

False

d['three'] = 3.0

d

{'one': 1, 'two': 2, 'three': 3.0}

d['three'] = [3, 3.0, 'drei']

d

{'one': 1, 'two': 2, 'three': [3, 3.0, 'drei']}

type(d)

dict

'four' in d

False

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

'four' <class 'KeyError'>

elem = d.get('four')
if elem is None:
    elem = 4
print(elem)

4

elem = d.get('four', 4)
print(elem)

4

Exercise: Mixed List, Interactive Interpreter

l = []

l.append(42)

l

[42]

l.append(42.666)
l.append(True)
l.append('abc')

l

[42, 42.666, True, 'abc']

l.append([1,2,'drei'])

l

[42, 42.666, True, 'abc', [1, 2, 'drei']]

l.append((1, 2, 'drei'))

l

[42, 42.666, True, 'abc', [1, 2, 'drei'], (1, 2, 'drei')]

l.append({1,2,3})

l

[42, 42.666, True, 'abc', [1, 2, 'drei'], (1, 2, 'drei'), {1, 2, 3}]

l.append({1:'one', 2:'two'})

l

[42,
 42.666,
 True,
 'abc',
 [1, 2, 'drei'],
 (1, 2, 'drei'),
 {1, 2, 3},
 {1: 'one', 2: 'two'}]

len(), range(), for

len(l)

8

for elem in l:
    print(elem)

42
42.666
True
abc
[1, 2, 'drei']
(1, 2, 'drei')
{1, 2, 3}
{1: 'one', 2: 'two'}

l = [0,1,2,3,4]
for elem in l:
    print(elem)

0
1
2
3
4

for elem in range(5):
    print(elem)

0
1
2
3
4

elem = 0
while elem < 5:
    print(elem)
    elem += 1

0
1
2
3
4

d

{'one': 1, 'two': 2, 'three': [3, 3.0, 'drei']}

for k in d:
    print(k)

one
two
three

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

one
two
three

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

1
2
[3, 3.0, 'drei']

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

('one', 1)
('two', 2)
('three', [3, 3.0, 'drei'])

for elem in d.items():
    k = elem[0]
    v = elem[1]
    print('key: ', k, ', value: ', v)

key:  one , value:  1
key:  two , value:  2
key:  three , value:  [3, 3.0, 'drei']

for k, v in d.items():
    print('key: ', k, ', value: ', v)

key:  one , value:  1
key:  two , value:  2
key:  three , value:  [3, 3.0, 'drei']

References, (Im)mutability

a = 42

id(a)

140640823526928

b = a

id(b)

140640823526928

id(a) == id(b)

True

a is b

True

a == b

True

l1 = [1, 2, 3]

id(l1)

140640722624768

l2 = [1, 2, 3]

id(l2)

140640722715136

l1.append(4)

l1

[1, 2, 3, 4]

l2

[1, 2, 3]

l1 is l2

False

l1

[1, 2, 3, 4]

l1_copy = l1

l1_copy is l1

True

id(l1_copy) == id(l1)

True

l1.append(5)

l1

[1, 2, 3, 4, 5]

l1_copy

[1, 2, 3, 4, 5]

Generators, yield

l = [1, 2, 3]

for elem in l:
    print(elem)

1
2
3

it = iter(l)

next(it)

1

next(it)

2

next(it)

3

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

 <class 'StopIteration'>

s = 'abc'

for elem in s:
    print(elem)

a
b
c

l = list()

l

[]

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

l

[1, 2, 3]

l = [1, 2, 3]

l = list(range(1, 4))

l

[1, 2, 3]

for elem in range(4):
    print(elem)

0
1
2
3

for elem in range(2, 4):
    print(elem)

2
3

def my_funky_generator():
    print('bis zum ersten')
    yield 1
    print('bis zum zweiten')
    yield 2
    print('bis zum dritten')
    yield 3
    print('und aus')

meine_dumme_sequenz = my_funky_generator()

type(meine_dumme_sequenz)

generator

it = iter(meine_dumme_sequenz)

next(it)

bis zum ersten

1

next(it)

bis zum zweiten

2

next(it)

bis zum dritten

3

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

und aus
 <class 'StopIteration'>

for elem in my_funky_generator():
    print(elem)

bis zum ersten
1
bis zum zweiten
2
bis zum dritten
3
und aus

def my_range(end):
    cur = 0
    while cur < end:
        yield cur
        cur += 1

for elem in my_range(4):
    print(elem)

0
1
2
3

Other -ables: Callable

print('hallo')

hallo

type(print)

builtin_function_or_method

type(list)

type

list()

[]

def f():
    print('hallo f()')

f()

hallo f()

type(f)

function

f.__call__

<method-wrapper '__call__' of function object at 0x7fe9785083a0>

f.__call__()

hallo f()

list.__call__

<method-wrapper '__call__' of type object at 0x7fe98c21bce0>

list.__call__('abc')

['a', 'b', 'c']

list('abc')

['a', 'b', 'c']

class Greeter:
    def __call__(self, s):
        print('hallo', s)

g = Greeter()

type(g)

__main__.Greeter

g('Joerg')

hallo Joerg

g.__call__

<bound method Greeter.__call__ of <__main__.Greeter object at 0x7fe9796976d0>>

g.__call__('Joerg')

hallo Joerg

Indexing and Slicing

l = [1, 2, [3, 4, 5], 6, 7]
l[2]

[3, 4, 5]

l[2][1]

4

l[2:3] = l[2]

l

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

References, (Im)mutability

a = 42

id(a)

140640823526928

a += 1

id(a)

140640823526960

t = (1, 'eins')

id(t)

140640740502720

try:
    t.append(3)
except Exception as e:
    print(e, type(e))

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

t += (2, 'zwei')

id(t)

140640722823952

t

(1, 'eins', 2, 'zwei')

l = [1, 2, 3]

id(l)

140640741119552

l += [4, 5, 6]

id(l)

140640741119552

l

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

l_copy = l[:]

l_copy

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

id(l_copy)

140640741312256

l_copy is l

False

l1 = [1, [2, 3, 4], 5]

l2 = l1[:]

l2

[1, [2, 3, 4], 5]

l2 is not l1

True

l2[1].append(666)

l2

[1, [2, 3, 4, 666], 5]

l1

[1, [2, 3, 4, 666], 5]

l1[1] is l2[1]

True

import copy

l1

[1, [2, 3, 4, 666], 5]

id(l1)

140640722734080

id(l1[1])

140640722760768

l3 = copy.deepcopy(l1)

id(l3)

140640722739712

id(l3[1])

140640741402496

exec() (and eval())

code = '''
b = 666
print('hallo')
'''

exec(code)

hallo

b

666

context = {}
exec(code, context)

hallo

b

666

del b

context['b']

666

More About Strings

"abc"

'abc'

'abc'

'abc'

'don\'t'

"don't"

"don't"

"don't"

Raw Strings

s = "C:\path\to\nowhere"

print(s)

C:\path o
owhere

s = r"C:\path\to\nowhere"
print(s)

C:\path\to\nowhere

import re

line = "   666 |    Joerg    |Faschingbauer   "

regex = re.compile(r'^\s*(\d+)\s*|\s*([A-Za-z]+)\s*|\s*([A-Za-z]+)\s*$')

match = regex.search(line)

match.group(1)

'666'

Formatting (f-Strings)

a = 42
b = 666

'a hat den Wert '+str(a)+', und b hat den Wert '+str(b)

'a hat den Wert 42, und b hat den Wert 666'

f'a hat den Wert {a:07}, und b hat den Wert {b}'

'a hat den Wert 0000042, und b hat den Wert 666'

Miscellaneous String Methods

s = '666'

s.isdigit()

True

'abc'.isdigit()

False

'abc'.isalpha()

True

'abc'.isidentifier()

True

'666'.isidentifier()

False

'mississippi'.count('ss')

2

'file.csv'.endswith('.csv')

True

'mississippi'.find('ss')

2

'mississippi'.find('xx')

-1

'mississippi'.rfind('ss')

5

line = "   666 |    Joerg    |Faschingbauer   "

line.split('|')

['   666 ', '    Joerg    ', 'Faschingbauer   ']

'   666        '.strip()

'666'

'   666        '.lstrip()

'666        '

'   666        '.rstrip()

'   666'

line = "   666 |    Joerg    |Faschingbauer   "

[elem.strip() for elem in line.split('|')]

['666', 'Joerg', 'Faschingbauer']

elems = ['666', 'Joerg', 'Faschingbauer']
'|'.join(elems)

'666|Joerg|Faschingbauer'

line = "   666 |    Joerg    |Faschingbauer   "

svnr, firstname, lastname = [elem.strip() for elem in line.split('|')]

svnr, firstname, lastname

('666', 'Joerg', 'Faschingbauer')

More About Lists

l = [1, 2, 'drei']

l.append(4.0)

l

[1, 2, 'drei', 4.0]

l.extend([3, 4, 5])

l

[1, 2, 'drei', 4.0, 3, 4, 5]

l.extend(range(10, 15))

l

[1, 2, 'drei', 4.0, 3, 4, 5, 10, 11, 12, 13, 14]

l.extend('abc')

l

[1, 2, 'drei', 4.0, 3, 4, 5, 10, 11, 12, 13, 14, 'a', 'b', 'c']

l.insert(3, 3.5)

l

[1, 2, 'drei', 3.5, 4.0, 3, 4, 5, 10, 11, 12, 13, 14, 'a', 'b', 'c']

l.insert(0, -1)

l

[-1, 1, 2, 'drei', 3.5, 4.0, 3, 4, 5, 10, 11, 12, 13, 14, 'a', 'b', 'c']

l.pop(3)

'drei'

del l[1]

l = [45, 2, 3, 9, 1]

l.sort()

l

[1, 2, 3, 9, 45]

l = [45, 2, 3, 9, 1]

sorted(l)

[1, 2, 3, 9, 45]

l

[45, 2, 3, 9, 1]

l.reverse()

l

[1, 9, 3, 2, 45]

More About Dictionaries

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

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

l = [('one',1), ('two', 2)]
d = dict(l)

d

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

d['three'] = 3

d

{'one': 1, 'two': 2, 'three': 3}

d['three'] = 3.0

d

{'one': 1, 'two': 2, 'three': 3.0}

del d['three']

'three' in d

False

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

'three' <class 'KeyError'>

value = d.get('three')
if value is None:
    print('bled, aber, waere doch wohl', 3)
else:
    print('jo eh,', value)

bled, aber, waere doch wohl 3

value = d.get('three', 3)
print(value)

3

if 'three' in d:
    value = d['three']
else:
    value = 3
    d['three'] = value
print(value)

3

del d['three']

value = d.setdefault('three', 3)
print(value)

3

d

{'one': 1, 'two': 2, 'three': 3}

other = {'three': 3.0, 'four': 4.0}

d.update(other)

d

{'one': 1, 'two': 2, 'three': 3.0, 'four': 4.0}

More About Sets

s = {1,2,3}

l = [1, 2, 3]

s = set(l)

s

{1, 2, 3}

s = set('abc')
s

{'a', 'b', 'c'}

s = set(range(5))
s

{0, 1, 2, 3, 4}

2 in s

True

s.remove(2)
s

{0, 1, 3, 4}

s.add(2)

s

{0, 1, 2, 3, 4}

s1 = set(range(4))
s2 = set(range(3, 8))

s1, s2

({0, 1, 2, 3}, {3, 4, 5, 6, 7})

s1 | s2

{0, 1, 2, 3, 4, 5, 6, 7}

s1 & s2

{3}

s1 ^ s2

{0, 1, 2, 4, 5, 6, 7}

s1 < s2

False

s1 <= s2

False

Encoding

s = 'Liebe Grüße, Jörg'

type(s)

str

try:
    s.encode(encoding='ascii')
except Exception as e:
    print(e, type(e))

'ascii' codec can't encode characters in position 8-9: ordinal not in range(128) <class 'UnicodeEncodeError'>

b = s.encode(encoding='iso-8859-1')

b

b'Liebe Gr\xfc\xdfe, J\xf6rg'

type(b)

bytes

b.decode(encoding='iso-8859-5')

'Liebe Grќпe, Jіrg'

print(b)

b'Liebe Gr\xfc\xdfe, J\xf6rg'

lg = '祝好'

type(lg)

str

len(lg)

2

lg.encode(encoding='big5')

b'\xaf\xac\xa6n'

len(lg.encode(encoding='big5'))

4

unterschrift = lg + ' Jörg'

unterschrift

'祝好 Jörg'

try:
    unterschrift.encode('iso-8859-1')
except Exception as e:
    print(e, type(e))

'latin-1' codec can't encode characters in position 0-1: ordinal not in range(256) <class 'UnicodeEncodeError'>

try:
    unterschrift.encode('big5')
except Exception as e:
    print(e, type(e))

'big5' codec can't encode character '\xf6' in position 4: illegal multibyte sequence <class 'UnicodeEncodeError'>

unterschrift.encode('utf-8')

b'\xe7\xa5\x9d\xe5\xa5\xbd J\xc3\xb6rg'

unterschrift.encode('utf-16')

b'\xff\xfe]y}Y \x00J\x00\xf6\x00r\x00g\x00'

unterschrift.encode('utf-32')

b'\xff\xfe\x00\x00]y\x00\x00}Y\x00\x00 \x00\x00\x00J\x00\x00\x00\xf6\x00\x00\x00r\x00\x00\x00g\x00\x00\x00'