Python Basics (2023-12-18 - 2023-12-20)

for i in range(5):
    print(i)
    print(i+2)
print('habe fertig')

0
2
1
3
2
4
3
5
4
6
habe fertig

was jetzt geschehen wird

j = 42

j

42

type(j)

int

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

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

type(j)

int

j = [1, 2, 3]

type(j)

list

j = 42.45

type(j)

float

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

translation_table['one']

1

2**1000

10715086071862673209484250490600018105614048117055336074437503883703510511249361224931983788156958581275946729175531468251871452856923140435984577574698574803934567774824230985421074605062371141877954182153046474983581941267398767559165543946077062914571196477686542167660429831652624386837205668069376

if 1 == '1':
    print('ja')
else:
    print('nein')

nein

def max(a, b):
    '''
    das ist eine hochkomplexe blah
    blah
    bla

    '''
    return a + b

max(1, 2)

3

max.__doc__

'\n    das ist eine hochkomplexe blah\n    blah\n    bla\n\n    '

help(max)

Help on function max in module __main__:

max(a, b)
    das ist eine hochkomplexe blah
    blah
    bla

type(max)

function

type(j)

float

j = max

type(j)

function

j(1, 2)

3

import sys

sys.argv

['/home/jfasch/venv/jfasch-home/lib64/python3.10/site-packages/ipykernel_launcher.py',
 '-f',
 '/home/jfasch/.local/share/jupyter/runtime/kernel-98f8b9be-ad8f-4023-81a2-d1dc67d0282c.json']

sys.platform

'linux'

sys.path

['/home/jfasch/work/jfasch-home/trainings/log/detail/2023-12-18--Python-Basics',
 '/usr/lib64/python310.zip',
 '/usr/lib64/python3.10',
 '/usr/lib64/python3.10/lib-dynload',
 '',
 '/home/jfasch/venv/jfasch-home/lib64/python3.10/site-packages',
 '/home/jfasch/venv/jfasch-home/lib/python3.10/site-packages',
 '/home/jfasch/venv/jfasch-home/lib64/python3.10/site-packages/IPython/extensions',
 '/home/jfasch/.ipython']

type(sys)

module

sys = 666

try:
    sys.argv
except Exception as e:
    print(type(e), e)

<class 'AttributeError'> 'int' object has no attribute 'argv'

Variables

a = 42

type(a)

int

a = 1.5

type(a)

float

a = ['blah', 1.5]

type(a)

list

a, b, c = 1, 'eins', 1.0

a

1

b

'eins'

c

1.0

a, b = 1, 2

a

1

b

2

tmp = a

a = b

b = tmp

a

2

b

1

a, b = 1, 2

a, b = b, a

a

2

b

1

(a, b) = (b, a)

a = 42

id(a)

139783143835152

hex(id(a))

'0x7f21cca24610'

b = a

id(b)

139783143835152

id(a) == id(b)

True

a is b

True

Datatypes

Integers

i = 42

i = -42

i = 2**64-1

bin(i)

'0b1111111111111111111111111111111111111111111111111111111111111111'

len(bin(i))

66

i += 1

len(bin(i))

67

bin(i)

'0b10000000000000000000000000000000000000000000000000000000000000000'

i

18446744073709551616

i += 2**100

bin(i)

'0b10000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000000'

1_000_000

1000000

3/2

1.5

3//2

1

3//2

1

3%2

1

16/4

4.0

16%4

0

17%4

1

2**3

8

(3**2)-1

8

Datatype Conversion

i = 42

j = 42.666

i = j

i

42.666

i = 42

s = 'abc'

type(s)

str

i

42

s = str(i)

s

'42'

j = int(s)

j

42

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

<class 'ValueError'> invalid literal for int() with base 10: 'abc'

int('abc', 16)

2748

try:
    int('42.666')
except Exception as e:
    print(type(e), e)

<class 'ValueError'> invalid literal for int() with base 10: '42.666'

float('42.666')

42.666

s = 'abc'

if type(s) is str:
    print('jo')

jo

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

str(d)

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

int('12345', 7)

3267

Compound Datatypes

List

l = [1, 2, 3]

l

[1, 2, 3]

len(l)

3

l.append('vier')

l

[1, 2, 3, 'vier']

l.append(5.0)

l

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

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

len(l)

6

l

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

l.append(l)

len(l)

7

l

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

l[0]

1

l[6]

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

l[-1]

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

l[-2]

[6, 7, 'acht']

l[4]

5.0

l[-3]

5.0

del l[-1]

l

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

l.extend([10, 20, 30])

l

[1, 2, 3, 'vier', 5.0, [6, 7, 'acht'], 10, 20, 30]

try:
    l.sort()
except Exception as e:
    print(type(e), e)

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

l

[1, 2, 3, 'vier', 5.0, [6, 7, 'acht'], 10, 20, 30]

l1 = [1, 2, 3]

l1.extend([4, 5, 6])

l1

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

l1.extend(l1)

l1

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

l1.sort()

l1

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

l1 = [1,2,3]

l1

[1, 2, 3]

l2 = [3, 4, [5, 6, 7]]

l1.extend(l2)

l1

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

l2[-1]

[5, 6, 7]

l2[-1].append(666)

l2

[3, 4, [5, 6, 7, 666]]

l1

[1, 2, 3, 3, 4, [5, 6, 7, 666]]

l = [3, 1, 2, 4, 5, 88, 42]

3 in l

True

2 in l

True

666 in l

False

Tuple

l = [1, 2, 3]

id(l)

139782834179584

l.append(4)

id(l)

139782834179584

i = 42

id(i)

139783143835152

i += 1

i

43

id(i)

139783143835184

t = (1, 2, 3)

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

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

t[1]

2

try:
    t[1] += 5
except Exception as e:
    print(type(e), e)

<class 'TypeError'> 'tuple' object does not support item assignment

t = (1, 2, [3, 4])

t[2]

[3, 4]

t[2].append(666)

t

(1, 2, [3, 4, 666])

try:
    t[0] = 7
except Exception as e:
    print(type(e), e)

<class 'TypeError'> 'tuple' object does not support item assignment

Dictionary

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

d['one']

1

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

<class 'KeyError'> 'three'

d['three'] = 3

'three' in d

True

d1 = {
    'three': 33,
    'four': 'vier'
}

d.update(d1)

d

{'one': 1, 'two': 2, 'three': 33, 'four': 'vier'}

d = {}

type(d)

dict

d = dict()

type(d)

dict

Set

menge = {1, 2, 3}

menge.add(4)

menge.add('fuenf')

menge

{1, 2, 3, 4, 'fuenf'}

menge.remove(2)

menge

{1, 3, 4, 'fuenf'}

4 in menge

True

menge.add(5)

menge

{1, 3, 4, 5, 'fuenf'}

menge.remove(5)

menge

{1, 3, 4, 'fuenf'}

m1 = {1, 2, 3, 4}

m2 = {3, 4, 5, 6}

m1 | m2

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

m1 & m2

{3, 4}

m1 - m2

{1, 2}

m2 - m1

{5, 6}

type(m2)

set

3 in m1

True

leeres_set = set()

Boolean

b = True

type(b)

bool

i = 666

bool(i)

True

bool(0)

False

bool('')

False

l = []
len(l)

0

bool(l)

False

l = None

type(l)

NoneType

l = []

if l:
    print('jo')
else:
    print('na')

na

if len(l):
    print('jo')
else:
    print('na')

na

if len(l) == 0:
    print('jo')
else:
    print('na')

jo

Weirdness (Comprehensions)

List Comprehension

numbers = [0, 1, 2, 3, 4, 5]

squares = []
for n in numbers:
    squares.append(n**2)

squares

[0, 1, 4, 9, 16, 25]

[n**2 for n in numbers]

[0, 1, 4, 9, 16, 25]

Dictionary Comprehension (Exchange key and Value of dict)

d = {'zero': 0, 'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5, 'six': 6, 'seven': 7, 'eight': 8, 'nine': 9}

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

0
1
2
3
4
5
6
7
8
9

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

0
1
2
3
4
5
6
7
8
9

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

('zero', 0)
('one', 1)
('two', 2)
('three', 3)
('four', 4)
('five', 5)
('six', 6)
('seven', 7)
('eight', 8)
('nine', 9)

for item in d.items():
    k = item[0]
    v = item[1]
    print(k, v)

zero 0
one 1
two 2
three 3
four 4
five 5
six 6
seven 7
eight 8
nine 9

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

zero 0
one 1
two 2
three 3
four 4
five 5
six 6
seven 7
eight 8
nine 9

d_reversed = {}

for k, v in d.items():
    d_reversed[v] = k

d_reversed

{0: 'zero',
 1: 'one',
 2: 'two',
 3: 'three',
 4: 'four',
 5: 'five',
 6: 'six',
 7: 'seven',
 8: 'eight',
 9: 'nine'}

d_reversed = {v:k for k, v in d.items()}

d_reversed

{0: 'zero',
 1: 'one',
 2: 'two',
 3: 'three',
 4: 'four',
 5: 'five',
 6: 'six',
 7: 'seven',
 8: 'eight',
 9: 'nine'}

Functional Programming

l = [0, 1, 2, 3, 4, 5]

def square(n):
    return n**2

for s in map(square, l):
    print(s)

0
1
4
9
16
25

for s in map(lambda n: n**2, l):
    print(s)

0
1
4
9
16
25

for s in filter(lambda n: n%2==0, l):
    print(s)

0
2
4

d

{'zero': 0,
 'one': 1,
 'two': 2,
 'three': 3,
 'four': 4,
 'five': 5,
 'six': 6,
 'seven': 7,
 'eight': 8,
 'nine': 9}

l1 = [1, 2, 3]
l2 = ['one', 'two', 'three']

for elem in zip(l1, l2):
    print(elem)

(1, 'one')
(2, 'two')
(3, 'three')

for elem in zip(d.keys(), d.values()):
    print(elem)

('zero', 0)
('one', 1)
('two', 2)
('three', 3)
('four', 4)
('five', 5)
('six', 6)
('seven', 7)
('eight', 8)
('nine', 9)

for elem in zip(d.values(), d.keys()):
    print(elem)

(0, 'zero')
(1, 'one')
(2, 'two')
(3, 'three')
(4, 'four')
(5, 'five')
(6, 'six')
(7, 'seven')
(8, 'eight')
(9, 'nine')

{v: k for v, k in zip(d.values(), d.keys())}

{0: 'zero',
 1: 'one',
 2: 'two',
 3: 'three',
 4: 'four',
 5: 'five',
 6: 'six',
 7: 'seven',
 8: 'eight',
 9: 'nine'}

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

dict(l)

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

dict(zip(d.values(), d.keys()))

{0: 'zero',
 1: 'one',
 2: 'two',
 3: 'three',
 4: 'four',
 5: 'five',
 6: 'six',
 7: 'seven',
 8: 'eight',
 9: 'nine'}

set(), list(), dict()

l = [2, 4, 10, 9, 1]

s = set(l)

s

{1, 2, 4, 9, 10}

list(s)

[1, 2, 4, 9, 10]

s1 = {2, 3, 4}
s2 = {4, 5, 6}

s1 - s2

{2, 3}

set(s1|s2)

{2, 3, 4, 5, 6}

set(s1 - s2)

{2, 3}

diff = s1 - s2

diff

{2, 3}

set(diff)

{2, 3}

while (and else)

Summe von 1..100 (beide inklusive)

summe = 0
n = 1
while n <= 100:
    summe += n
    n += 1
print(summe)

5050

sum(range(1, 101))     # <--- pythonic

5050

int(100*101/2)

5050

import random

while True:
    eyes = random.randrange(1, 7)
    if eyes == 6:
        print('yaay')
        break
    else:
        print('lose', eyes)

lose 4
yaay

n_tries = 0
while n_tries < 8:
    eyes = random.randrange(1, 7)
    if eyes == 6:
        print('yaay')
        break
    else:
        print('lose in versuch', n_tries, ',', eyes)
    n_tries += 1
else:
    print('kompletter lose')

lose in versuch 0 , 1
lose in versuch 1 , 3
lose in versuch 2 , 1
lose in versuch 3 , 1
lose in versuch 4 , 5
lose in versuch 5 , 3
lose in versuch 6 , 4
lose in versuch 7 , 3
kompletter lose

range()

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

0
1
2
3
4

for elem in l:
    print('hallo')

hallo
hallo
hallo
hallo
hallo

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

0
1
2
3
4

for elem in range(2, 10):
    print(elem)

2
3
4
5
6
7
8
9

for elem in range(2, 10, 2):
    print(elem)

2
4
6
8

range(), And Generators, The Iterator Protocol

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

0
1
2
3
4

print(type(l))

<class 'list'>

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

0
1
2
3
4

r

range(0, 5)

print(type(r))

<class 'range'>

for elem in r:
    print(elem)

0
1
2
3
4

for elem in l:
    print(elem)

0
1
2
3
4

it = iter(l)

print(type(it))

<class 'list_iterator'>

next(it)

0

next(it)

1

next(it)

2

next(it)

3

next(it)

4

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

<class 'StopIteration'>

r = range(3)

it = iter(r)

next(it)

0

def foo(bar):
    return bar**2

def my_deppertes_range():
    print('start')
    yield 0
    print('yield 1')
    yield 1
    print('yield 2')
    yield 2
    print('end')

mdr = my_deppertes_range()
for elem in mdr:
    print('got', elem)

start
got 0
yield 1
got 1
yield 2
got 2
end

mdr = my_deppertes_range()

it = iter(mdr)

next(it)

start

0

next(it)

yield 1

1

next(it)

yield 2

2

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

end
<class 'StopIteration'>

numbers = range(20)

def even(seq):
    for n in seq:
        if n%2 == 0:
            yield n

for elem in even(numbers):
    print(elem)

0
2
4
6
8
10
12
14
16
18

Functions

def maximum(a, b):
    '''
    blah

    * a: links
    * b: rechts
    '''

    if a < b:
        return b
    return a

maximum(1, 2)

2

maximum('aaa', 'bbb')

'bbb'

i = 666
print(type(i))

<class 'int'>

print(type(maximum))

<class 'function'>

i = maximum

i(1, 2)

2

Return Value? Parameters?

def foo():
    return True

x = foo()

x

True

if foo():
    print('ja')
else:
    print('nein')

ja

def foo():
    return False

if foo():
    print('ja')
else:
    print('nein')

nein

def is_even(number):
    if number % 2 == 0:
        return True
    else:
        return False

if is_even(9):
    print('ja')
else:
    print('nein')

nein

is_even(10)

True

More About Datatypes

References, Immutability

Integer objeckte sind Singletons bis 256 (?)

a = 42

id(a)

139783143835152

b = 42

id(b)

139783143835152

l1 = [1, 2, 3]

id(l1)

139782799029888

l2 = [1, 2, 3]

id(l2)

139782798781696

a = 666

id(a)

139782798895952

b = 666

id(b)

139782798895792

a = 42

id(a)

139783143835152

a += 1

id(a)

139783143835184

def foo(n):
    n += 1

a

43

foo(a)

a

43

l = [1,2,3]

def foo(seq):
    seq.append(666)

foo(l)

l

[1, 2, 3, 666]

t = (1,2,3)

try:
    foo(t)
except Exception as e:
    print(type(e), e)

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

Und Schuetzen?

l1 = [1, 2, 3]
def avg(seq):
    rv = sum(seq)/len(seq)
    seq.append(666)
    return rv

avg(l1)

2.0

l1

[1, 2, 3, 666]

l1 = [1, 2, 3]

id(l1)

139782798980096

l1_copy = l1[:]

avg(l1_copy)

2.0

l1 = [1, 2, ['abc', 'def'], 3, 4]

l2 = l1[:]

l1 is l2

False

l2.append(666)

l1

[1, 2, ['abc', 'def'], 3, 4]

l2

[1, 2, ['abc', 'def'], 3, 4, 666]

l2[2].append('ghi')

l2

[1, 2, ['abc', 'def', 'ghi'], 3, 4, 666]

l1

[1, 2, ['abc', 'def', 'ghi'], 3, 4]

t1 = (1, 2, ['abc', 'def'], 3, 4)

t2 = t1[:4]

t1 is t2

False

t1[2] is t2[2]

True

t2[2].append('teifl')

t1

(1, 2, ['abc', 'def', 'teifl'], 3, 4)

More About Strings

s = 'blah'

s

'blah'

s = "blah"

s

'blah'

'Es ist Joerg\'s Schuld'

"Es ist Joerg's Schuld"

"Es ist Joerg's Schuld"

"Es ist Joerg's Schuld"

"erste zeile\nzweite zeile"

'erste zeile\nzweite zeile'

print("erste zeile\nzweite zeile")

erste zeile
zweite zeile

print("a\tb")

a       b

print("a\\b")

a\b

dos_path = "C:\Programs\Meine Programme\neues programm"

print(dos_path)

C:\Programs\Meine Programme
eues programm

dos_path = "C:\Programs\Meine Programme\\neues programm"

print(dos_path)

C:\Programs\Meine Programme\neues programm

dos_path = r"C:\Programs\Meine Programme\neues programm"

print(dos_path)

C:\Programs\Meine Programme\neues programm

Formatting

"blah %d blah" % 666

'blah 666 blah'

"blah %d blah %.6f" % (666, 42.3)

'blah 666 blah 42.300000'

'blah {0} blah {1} blah {0}'.format(666, 42.3)

'blah 666 blah 42.3 blah 666'

'blah {a} blah {b} blah {a}'.format(b=666, a=42.3)

'blah 42.3 blah 666 blah 42.3'

a, b = 42.3, 666

f'blah {a} blah {b} {a}'

'blah 42.3 blah 666 42.3'

f'blah {a+1}'

'blah 43.3'

f'blah {[i**2 for i in range(5)]}'

'blah [0, 1, 4, 9, 16]'

Regular Expressions

line = '     666         ; Joerg     ;Faschingbauer      '

pattern = r'^\s*(\d+)\s*;\s*([A-Za-z]+)\s*;\s*([A-Za-z]+)\s*$'

print(pattern)

^\s*(\d+)\s*;\s*([A-Za-z]+)\s*;\s*([A-Za-z]+)\s*$

import re

compiled_pattern = re.compile(pattern)

match = compiled_pattern.search(line)

match.group(1)

'666'

match.group(2)

'Joerg'

match.group(3)

'Faschingbauer'

Das gleich ohne regex

line.split(';')

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

fields = []
for field in line.split(';'):
    fields.append(field.strip())
fields

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

[field.strip() for field in line.split(';')]

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

Miscellaneous String Methods

s = '      '
s.isspace()

True

'XXX'.isupper()

True

'xxx'.islower()

True

'666'.isdigit()

True

len('')

0

s = 'xxx'

if len(s):
    print('was drin')

was drin

if s:
    print('was drin')

was drin

s = ''

if s:
    print('was drin')
else:
    print('nix drin')

nix drin

s = 'mississippi'

s.count('ss')

2

s.upper()

'MISSISSIPPI'

s.find('ss')

2

s.find('ss', 2+1)

5

s.find('xxx')

-1

s.index('ss')

2

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

<class 'ValueError'> substring not found

filename = 'data.csv'

filename.endswith('.csv')

True

line

'     666         ; Joerg     ;Faschingbauer      '

line.split(';')

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

items = ['666', 'Joerg', 'Faschingbauer']

';'.join(items)

'666;Joerg;Faschingbauer'

'hallo'.center(80)

'                                     hallo                                      '

s = 'hallo'
' '*(80-len(s)) + s

'                                                                           hallo'

More About Lists

l = [1, 'two', 3.0]

l.append(666)

l

[1, 'two', 3.0, 666]

l1 = [8, 'neun']

l.extend(l1)
l

[1, 'two', 3.0, 666, 8, 'neun']

del l[3]

l

[1, 'two', 3.0, 8, 'neun']

l[2]

3.0

l.insert(0, -1)

l

[-1, 1, 'two', 3.0, 8, 'neun']

l.insert(2, 1.5)
l

[-1, 1, 1.5, 'two', 3.0, 8, 'neun']

l.reverse()
l

['neun', 8, 3.0, 'two', 1.5, 1, -1]

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

-1
1
1.5
two
3.0
8
neun

l.pop(5)

1

l

['neun', 8, 3.0, 'two', 1.5, -1]

More About Dictionaries

d = dict()

d

{}

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

d = {}

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

d

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

d['one']

1

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

<class 'KeyError'> 'three'

v = d.get('two')
v

2

v = d.get('three')
print(v)

None

if d.get('three'):
    print('ja')
else:
    print('nein')

nein

d['three'] = 3

del d['three']

d['three'] = None

'three' in d

True

del d['three']

v = d.get('three')
if v is None:
    v = 3
v

3

v = d.get('three', 3)
v

3

v = d.get('three')
if v is None:
    d['three'] = 3
    v = d['three']
v

3

del d['three']

v = d.setdefault('three', 3)
v

3

d

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

for elem in d:
    print(elem)

one
two
three

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

one
two
three

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

1
2
3

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

('one', 1)
('two', 2)
('three', 3)

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

one 1
two 2
three 3

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

one 1
two 2
three 3

a, b = 1, 2

a

1

b

2

(a, b) = (b, a)

a

2

b

1

line = '666;Joerg;Faschingbauer'
id, firstname, lastname = line.split(';')

id

'666'

try:
    id(a)
except Exception as e:
    print(type(e), e)

<class 'TypeError'> 'str' object is not callable

int('666')

666

int = 666

try:
    int('666')
except Exception as e:
    print(type(e), e)

<class 'TypeError'> 'int' object is not callable

del int

a = 666

type(a)

int

int = type(a)

int('666')

666

__builtins__

<module 'builtins' (built-in)>

__builtin__.id

<function id(obj, /)>

id = __builtins__.id

id(a)

139782799135312

keys = [2, 3, 1, 5, 1]
dict.fromkeys(keys)

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

for k in dict.fromkeys(keys):
    print(k)

2
3
1
5

More About Sets

s = set('abc')
s

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

for elem in 'abc':
    print(elem)

a
b
c

set(['abc', 'def'])

{'abc', 'def'}

try:
    set(666)
except Exception as e:
    print(type(e), e)

<class 'TypeError'> 'int' object is not iterable

Comprehensions (Generator Expressions)

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

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

0
1
4
9
16

for elem in [i**2 for i in range(5)]:
    print(elem)

0
1
4
9
16

def squares(l):
    for elem in l:
        yield elem**2

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

0
1
4
9
16

for elem in (i**2 for i in range(5)):
    print(elem)

0
1
4
9
16

(i**2 for i in range(5))

<generator object <genexpr> at 0x7f21b81bbe60>

[i**2 for i in range(5)]

[0, 1, 4, 9, 16]

File I/O

import os

cwd = os.getcwd()

os.chdir('/etc')

os.getcwd()

'/etc'

os.listdir()

['extlinux.conf',
 'favicon.png',
 'grub2-efi.cfg',
 'grub2.cfg',
 'issue',
 'issue.net',
 'opensc-x86_64.conf',
 '.java',
 'NetworkManager',
 'PackageKit',
 'UPower',
 'X11',
 'abrt',
 'alsa',
 'alternatives',
 'anaconda',
 'audit',
 'authselect',
 'avahi',
 'bash_completion.d',
 'binfmt.d',
 'bluetooth',
 'brltty',
 'ceph',
 'chkconfig.d',
 'chromium',
 'cifs-utils',
 'containers',
 'crypto-policies',
 'cups',
 'cupshelpers',
 'dbus-1',
 'dconf',
 'debuginfod',
 'default',
 'depmod.d',
 'dhcp',
 'dnf',
 'dnsmasq.d',
 'dracut.conf.d',
 'egl',
 'exports.d',
 'firefox',
 'firewalld',
 'flatpak',
 'flexiblasrc.d',
 'fonts',
 'fwupd',
 'gcrypt',
 'gdbinit.d',
 'gdm',
 'geoclue',
 'glvnd',
 'gnupg',
 'groff',
 'grub.d',
 'gss',
 'gssproxy',
 'hp',
 'httpd',
 'iproute2',
 'iscsi',
 'issue.d',
 'java',
 'jvm-common',
 'jvm',
 'kdump',
 'kernel',
 'krb5.conf.d',
 'ld.so.conf.d',
 'libblockdev',
 'libibverbs.d',
 'libnl',
 'libpaper.d',
 'libreport',
 'libssh',
 'libvirt',
 'logrotate.d',
 'lvm',
 'mcelog',
 'mdevctl.d',
 'modprobe.d',
 'modules-load.d',
 'motd.d',
 'my.cnf.d',
 'ndctl.conf.d',
 'ndctl',
 'nftables',
 'openldap',
 'openvpn',
 'opt',
 'ostree',
 'pam.d',
 'pkcs11',
 'pkgconfig',
 'pki',
 'plymouth',
 'pm',
 'polkit-1',
 'popt.d',
 'ppp',
 'profile.d',
 'pulse',
 'qemu-ga',
 'qemu',
 'rc.d',
 'reader.conf.d',
 'request-key.d',
 'rpm',
 'rwtab.d',
 'samba',
 'sane.d',
 'sasl2',
 'security',
 'selinux',
 'sgml',
 'skel',
 'sos',
 'speech-dispatcher',
 'ssh',
 'ssl',
 'sssd',
 'statetab.d',
 'sudoers.d',
 'swid',
 'sysconfig',
 'sysctl.d',
 'systemd',
 'terminfo',
 'thermald',
 'tmpfiles.d',
 'tpm2-tss',
 'udev',
 'udisks2',
 'unbound',
 'vmware-tools',
 'vpnc',
 'vulkan',
 'wireplumber',
 'wpa_supplicant',
 'xdg',
 'xml',
 'yum.repos.d',
 'zfs-fuse',
 '.pwd.lock',
 'DIR_COLORS',
 'DIR_COLORS.lightbgcolor',
 'GREP_COLORS',
 'adjtime',
 'bindresvport.blacklist',
 'brlapi.key',
 'chrony.conf',
 'chrony.keys',
 'dleyna-renderer-service.conf',
 'dleyna-server-service.conf',
 'dracut.conf',
 'fprintd.conf',
 'fstab',
 'fuse.conf',
 'jwhois.conf',
 'libaudit.conf',
 'libuser.conf',
 'locale.conf',
 'login.defs',
 'magic',
 'mailcap',
 'man_db.conf',
 'mime.types',
 'mke2fs.conf',
 'nanorc',
 'netconfig',
 'papersize',
 'passwdqc.conf',
 'pinforc',
 'request-key.conf',
 'sestatus.conf',
 'shells',
 'sudoers',
 'tcsd.conf',
 'usb_modeswitch.conf',
 'vconsole.conf',
 'wgetrc',
 'xattr.conf',
 'crypttab',
 'machine-id',
 'machine-info',
 'localtime',
 'hostname',
 'mtab',
 'subuid-',
 'subgid-',
 'timidity.cfg',
 'timidity++.cfg',
 'openal',
 'vdpau_wrapper.cfg',
 'ld.so.conf',
 'rpc',
 'asound.conf',
 'krb5.conf',
 'idmapd.conf',
 'sysctl.conf',
 'logrotate.conf',
 'mtools.conf',
 'brltty.conf',
 'flexiblasrc',
 'ts.conf',
 'gdbinit',
 'rsyncd.conf',
 'anthy-unicode.conf',
 'kdump.conf',
 'Trolltech.conf',
 'my.cnf',
 'rygel.conf',
 'virc',
 'swtpm-localca.conf',
 'swtpm-localca.options',
 'swtpm_setup.conf',
 'uresourced.conf',
 'opensc.conf',
 'aliases',
 'environment',
 'ethertypes',
 'exports',
 'filesystems',
 'host.conf',
 'inputrc',
 'motd',
 'networks',
 'printcap',
 'profile',
 'protocols',
 'services',
 'csh.login',
 'hosts',
 'nfsmount.conf',
 'nfs.conf',
 'dnsmasq.conf',
 'resolv.conf',
 'nsswitch.conf',
 'group-',
 'gshadow-',
 'passwd-',
 'shadow-',
 'thunderbird',
 'rhashrc',
 'ImageMagick-6',
 'bashrc',
 'csh.cshrc',
 'gimp',
 'updatedb.conf',
 '.updated',
 'mplayer',
 'youtube-dl.conf',
 'appstream.conf',
 'mosquitto',
 'containerd',
 'docker',
 'at.deny',
 'lftp.conf',
 'shadow',
 'group',
 'gshadow',
 'subuid',
 'subgid',
 'passwd~',
 'passwd',
 'init.d',
 'rc0.d',
 'rc1.d',
 'rc2.d',
 'rc3.d',
 'rc4.d',
 'rc5.d',
 'rc6.d',
 'fedora-release',
 'os-release',
 'redhat-release',
 'system-release',
 'system-release-cpe',
 'inittab',
 'sudo.conf',
 'trusted-key.key',
 'makedumpfile.conf.sample',
 'sensors.d',
 'sensors3.conf',
 'ld.so.cache']

f = open('passwd', encoding='utf-8')

f

<_io.TextIOWrapper name='passwd' mode='r' encoding='utf-8'>

os.chdir(cwd)

os.getcwd()

'/home/jfasch/work/jfasch-home/trainings/log/detail/2023-12-18--Python-Basics'

f = open('/etc/passwd', encoding='utf-8')

f

<_io.TextIOWrapper name='/etc/passwd' mode='r' encoding='utf-8'>

f.read(5)

'root:'

f.read(5)

':root'

f.readline()

':/root:/bin/bash\n'

f.readline()

'bin:x:1:1:bin:/bin:/sbin/nologin\n'

f.read()

'daemon:x:2:2:daemon:/sbin:/sbin/nologin\nadm:x:3:4:adm:/var/adm:/sbin/nologin\nlp:x:4:7:lp:/var/spool/lpd:/sbin/nologin\nsync:x:5:0:sync:/sbin:/bin/sync\nshutdown:x:6:0:shutdown:/sbin:/sbin/shutdown\nhalt:x:7:0:halt:/sbin:/sbin/halt\nmail:x:8:12:mail:/var/spool/mail:/sbin/nologin\noperator:x:11:0:operator:/root:/sbin/nologin\ngames:x:12:100:games:/usr/games:/sbin/nologin\nftp:x:14:50:FTP User:/var/ftp:/sbin/nologin\nnobody:x:65534:65534:Kernel Overflow User:/:/sbin/nologin\ndbus:x:81:81:System message bus:/:/sbin/nologin\napache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin\ntss:x:59:59:Account used for TPM access:/dev/null:/sbin/nologin\nsystemd-network:x:192:192:systemd Network Management:/:/usr/sbin/nologin\nsystemd-oom:x:999:999:systemd Userspace OOM Killer:/:/usr/sbin/nologin\nsystemd-resolve:x:193:193:systemd Resolver:/:/usr/sbin/nologin\nqemu:x:107:107:qemu user:/:/sbin/nologin\npolkitd:x:998:997:User for polkitd:/:/sbin/nologin\navahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin\nunbound:x:997:995:Unbound DNS resolver:/etc/unbound:/sbin/nologin\nnm-openconnect:x:996:994:NetworkManager user for OpenConnect:/:/sbin/nologin\ngeoclue:x:995:993:User for geoclue:/var/lib/geoclue:/sbin/nologin\nusbmuxd:x:113:113:usbmuxd user:/:/sbin/nologin\ngluster:x:994:992:GlusterFS daemons:/run/gluster:/sbin/nologin\nrtkit:x:172:172:RealtimeKit:/proc:/sbin/nologin\nchrony:x:993:990::/var/lib/chrony:/sbin/nologin\nsaslauth:x:992:76:Saslauthd user:/run/saslauthd:/sbin/nologin\ndnsmasq:x:991:989:Dnsmasq DHCP and DNS server:/var/lib/dnsmasq:/sbin/nologin\nrpc:x:32:32:Rpcbind Daemon:/var/lib/rpcbind:/sbin/nologin\ncolord:x:990:988:User for colord:/var/lib/colord:/sbin/nologin\nrpcuser:x:29:29:RPC Service User:/var/lib/nfs:/sbin/nologin\nopenvpn:x:989:987:OpenVPN:/etc/openvpn:/sbin/nologin\nnm-openvpn:x:988:986:Default user for running openvpn spawned by NetworkManager:/:/sbin/nologin\npipewire:x:987:985:PipeWire System Daemon:/var/run/pipewire:/sbin/nologin\nabrt:x:173:173::/etc/abrt:/sbin/nologin\nflatpak:x:986:983:User for flatpak system helper:/:/sbin/nologin\ngdm:x:42:42:GNOME Display Manager:/var/lib/gdm:/sbin/nologin\ngnome-initial-setup:x:985:982::/run/gnome-initial-setup/:/sbin/nologin\nvboxadd:x:984:1::/var/run/vboxadd:/sbin/nologin\nsshd:x:74:74:Privilege-separated SSH:/usr/share/empty.sshd:/sbin/nologin\ntcpdump:x:72:72::/:/sbin/nologin\njfasch:x:1000:1000:Jörg Faschingbauer:/home/jfasch:/bin/bash\nsystemd-coredump:x:978:978:systemd Core Dumper:/:/usr/sbin/nologin\nsystemd-timesync:x:977:977:systemd Time Synchronization:/:/usr/sbin/nologin\nmosquitto:x:976:976:Mosquitto Broker:/etc/mosquitto:/sbin/nologin\n'

f.read()

''

f.seek(0)

0

f.read(5)

'root:'

f = open('/etc/passwd', encoding='utf-8')

for line in f:
    print(line)

root:x:0:0:root:/root:/bin/bash

bin:x:1:1:bin:/bin:/sbin/nologin

daemon:x:2:2:daemon:/sbin:/sbin/nologin

adm:x:3:4:adm:/var/adm:/sbin/nologin

lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin

sync:x:5:0:sync:/sbin:/bin/sync

shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown

halt:x:7:0:halt:/sbin:/sbin/halt

mail:x:8:12:mail:/var/spool/mail:/sbin/nologin

operator:x:11:0:operator:/root:/sbin/nologin

games:x:12:100:games:/usr/games:/sbin/nologin

ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin

nobody:x:65534:65534:Kernel Overflow User:/:/sbin/nologin

dbus:x:81:81:System message bus:/:/sbin/nologin

apache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin

tss:x:59:59:Account used for TPM access:/dev/null:/sbin/nologin

systemd-network:x:192:192:systemd Network Management:/:/usr/sbin/nologin

systemd-oom:x:999:999:systemd Userspace OOM Killer:/:/usr/sbin/nologin

systemd-resolve:x:193:193:systemd Resolver:/:/usr/sbin/nologin

qemu:x:107:107:qemu user:/:/sbin/nologin

polkitd:x:998:997:User for polkitd:/:/sbin/nologin

avahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin

unbound:x:997:995:Unbound DNS resolver:/etc/unbound:/sbin/nologin

nm-openconnect:x:996:994:NetworkManager user for OpenConnect:/:/sbin/nologin

geoclue:x:995:993:User for geoclue:/var/lib/geoclue:/sbin/nologin

usbmuxd:x:113:113:usbmuxd user:/:/sbin/nologin

gluster:x:994:992:GlusterFS daemons:/run/gluster:/sbin/nologin

rtkit:x:172:172:RealtimeKit:/proc:/sbin/nologin

chrony:x:993:990::/var/lib/chrony:/sbin/nologin

saslauth:x:992:76:Saslauthd user:/run/saslauthd:/sbin/nologin

dnsmasq:x:991:989:Dnsmasq DHCP and DNS server:/var/lib/dnsmasq:/sbin/nologin

rpc:x:32:32:Rpcbind Daemon:/var/lib/rpcbind:/sbin/nologin

colord:x:990:988:User for colord:/var/lib/colord:/sbin/nologin

rpcuser:x:29:29:RPC Service User:/var/lib/nfs:/sbin/nologin

openvpn:x:989:987:OpenVPN:/etc/openvpn:/sbin/nologin

nm-openvpn:x:988:986:Default user for running openvpn spawned by NetworkManager:/:/sbin/nologin

pipewire:x:987:985:PipeWire System Daemon:/var/run/pipewire:/sbin/nologin

abrt:x:173:173::/etc/abrt:/sbin/nologin

flatpak:x:986:983:User for flatpak system helper:/:/sbin/nologin

gdm:x:42:42:GNOME Display Manager:/var/lib/gdm:/sbin/nologin

gnome-initial-setup:x:985:982::/run/gnome-initial-setup/:/sbin/nologin

vboxadd:x:984:1::/var/run/vboxadd:/sbin/nologin

sshd:x:74:74:Privilege-separated SSH:/usr/share/empty.sshd:/sbin/nologin

tcpdump:x:72:72::/:/sbin/nologin

jfasch:x:1000:1000:Jörg Faschingbauer:/home/jfasch:/bin/bash

systemd-coredump:x:978:978:systemd Core Dumper:/:/usr/sbin/nologin

systemd-timesync:x:977:977:systemd Time Synchronization:/:/usr/sbin/nologin

mosquitto:x:976:976:Mosquitto Broker:/etc/mosquitto:/sbin/nologin

f = open('/etc/passwd', encoding='ascii')

try:
    for line in f:
        print(line)
except Exception as e:
    print(type(e), e)

<class 'UnicodeDecodeError'> 'ascii' codec can't decode byte 0xc3 in position 2440: ordinal not in range(128)

pathlib, os.path

directory = '/etc'
filename = 'passwd'

directory + '/' + filename

'/etc/passwd'

directory + os.sep + filename

'/etc/passwd'

os.path.join(directory, filename)

'/etc/passwd'

import pathlib

directory = pathlib.Path('/etc')

directory

PosixPath('/etc')

directory / filename

PosixPath('/etc/passwd')

Regexen

import re

rex = r'[^A-F]'

re.search(rex, 'X')

<re.Match object; span=(0, 1), match='X'>

re.search(rex, 'D')

rex = r'^\s*(#.*|$)'

re.search(rex, '       # xxx')

<re.Match object; span=(0, 12), match='       # xxx'>

re.search(rex, '        ')

<re.Match object; span=(0, 8), match='        '>

re.search(rex, '     kadjckk  # xxddjh')

distill.py

s = ' \t   abc  \n   \n'
s.strip()

'abc'

s = '        # blah    '
s.strip()

'# blah'

print('blah')

blah

print('blah\n')

blah

print('blah', end='blahblah')
print('blah')

blahblahblahblah

print('blah', end='')
print('blah')

blahblah