Notebook¶

More About Strings¶

[1]:

s = 'Hello World'
type(s)

[1]:

str

[2]:

'Hello World'

[2]:

'Hello World'

[3]:

print(s)

Hello World

[4]:

[4]:

'Hello World'

[5]:

'We don\'t have much money'

[5]:

"We don't have much money"

[6]:

"We don't have much money"

[6]:

"We don't have much money"

[7]:

"\"'"

[7]:

'"\''

[8]:

windows_path = 'C:\Windows\neue Festplatte'

[9]:

print(windows_path)

C:\Windows
eue Festplatte

[10]:

windows_path = 'C:\\Windows\\neue Festplatte'
print(windows_path)

C:\Windows\neue Festplatte

[11]:

windows_path = r'C:\Windows\neue Festplatte'
print(windows_path)

C:\Windows\neue Festplatte

[12]:

line = '   1234 Joerg  Faschingbauer    [Lehrer]  '

[13]:

regex = r'^\s*(\d+)\s+(\.+)\s+(\.+)\s+[(\.+)]\s*$'
import re
match = re.search(regex, line)
print(match)

None

Multiline Strings (docstrings?)

[14]:

s = '''Hello
World'''
print(s)

Hello
World

[15]:

# This function adds two values. These two values can be anything,
# but both values must support the '+' operator.

# Parameters:
# * a
# * b
# Return: a+b (of the same type that the '+' operator produces
# when ....)
def add(a, b):
    return a+b
print(add(1, 2))

[16]:

def add(a, b):
    '''
    This function adds two values. These two values can be anything,
    but both values must support the '+' operator.

    Parameters:
    * a
    * b
    Return: a+b (of the same type that the '+' operator produces
    when ....)
    '''
    return a+b
print(add(1, 2))

[17]:

add

[17]:

<function __main__.add(a, b)>

[18]:

add.__doc__

[18]:

"\n    This function adds two values. These two values can be anything, \n    but both values must support the '+' operator.\n\n    Parameters:\n    * a\n    * b\n    Return: a+b (of the same type that the '+' operator produces \n    when ....)\n    "

[19]:

help(add)

Help on function add in module __main__:

add(a, b)
    This function adds two values. These two values can be anything,
    but both values must support the '+' operator.

    Parameters:
    * a
    * b
    Return: a+b (of the same type that the '+' operator produces
    when ....)

[20]:

import sys
help(sys)

Help on built-in module sys:

NAME
    sys

MODULE REFERENCE
    https://docs.python.org/3.9/library/sys

    The following documentation is automatically generated from the Python
    source files.  It may be incomplete, incorrect or include features that
    are considered implementation detail and may vary between Python
    implementations.  When in doubt, consult the module reference at the
    location listed above.

DESCRIPTION
    This module provides access to some objects used or maintained by the
    interpreter and to functions that interact strongly with the interpreter.

    Dynamic objects:

    argv -- command line arguments; argv[0] is the script pathname if known
    path -- module search path; path[0] is the script directory, else ''
    modules -- dictionary of loaded modules

    displayhook -- called to show results in an interactive session
    excepthook -- called to handle any uncaught exception other than SystemExit
      To customize printing in an interactive session or to install a custom
      top-level exception handler, assign other functions to replace these.

    stdin -- standard input file object; used by input()
    stdout -- standard output file object; used by print()
    stderr -- standard error object; used for error messages
      By assigning other file objects (or objects that behave like files)
      to these, it is possible to redirect all of the interpreter's I/O.

    last_type -- type of last uncaught exception
    last_value -- value of last uncaught exception
    last_traceback -- traceback of last uncaught exception
      These three are only available in an interactive session after a
      traceback has been printed.

    Static objects:

    builtin_module_names -- tuple of module names built into this interpreter
    copyright -- copyright notice pertaining to this interpreter
    exec_prefix -- prefix used to find the machine-specific Python library
    executable -- absolute path of the executable binary of the Python interpreter
    float_info -- a named tuple with information about the float implementation.
    float_repr_style -- string indicating the style of repr() output for floats
    hash_info -- a named tuple with information about the hash algorithm.
    hexversion -- version information encoded as a single integer
    implementation -- Python implementation information.
    int_info -- a named tuple with information about the int implementation.
    maxsize -- the largest supported length of containers.
    maxunicode -- the value of the largest Unicode code point
    platform -- platform identifier
    prefix -- prefix used to find the Python library
    thread_info -- a named tuple with information about the thread implementation.
    version -- the version of this interpreter as a string
    version_info -- version information as a named tuple
    __stdin__ -- the original stdin; don't touch!
    __stdout__ -- the original stdout; don't touch!
    __stderr__ -- the original stderr; don't touch!
    __displayhook__ -- the original displayhook; don't touch!
    __excepthook__ -- the original excepthook; don't touch!

    Functions:

    displayhook() -- print an object to the screen, and save it in builtins._
    excepthook() -- print an exception and its traceback to sys.stderr
    exc_info() -- return thread-safe information about the current exception
    exit() -- exit the interpreter by raising SystemExit
    getdlopenflags() -- returns flags to be used for dlopen() calls
    getprofile() -- get the global profiling function
    getrefcount() -- return the reference count for an object (plus one :-)
    getrecursionlimit() -- return the max recursion depth for the interpreter
    getsizeof() -- return the size of an object in bytes
    gettrace() -- get the global debug tracing function
    setdlopenflags() -- set the flags to be used for dlopen() calls
    setprofile() -- set the global profiling function
    setrecursionlimit() -- set the max recursion depth for the interpreter
    settrace() -- set the global debug tracing function

FUNCTIONS
    __breakpointhook__ = breakpointhook(...)
        breakpointhook(*args, **kws)

        This hook function is called by built-in breakpoint().

    __displayhook__ = displayhook(object, /)
        Print an object to sys.stdout and also save it in builtins._

    __excepthook__ = excepthook(exctype, value, traceback, /)
        Handle an exception by displaying it with a traceback on sys.stderr.

    __unraisablehook__ = unraisablehook(unraisable, /)
        Handle an unraisable exception.

        The unraisable argument has the following attributes:

        * exc_type: Exception type.
        * exc_value: Exception value, can be None.
        * exc_traceback: Exception traceback, can be None.
        * err_msg: Error message, can be None.
        * object: Object causing the exception, can be None.

    addaudithook(hook)
        Adds a new audit hook callback.

    audit(...)
        audit(event, *args)

        Passes the event to any audit hooks that are attached.

    call_tracing(func, args, /)
        Call func(*args), while tracing is enabled.

        The tracing state is saved, and restored afterwards.  This is intended
        to be called from a debugger from a checkpoint, to recursively debug
        some other code.

    exc_info()
        Return current exception information: (type, value, traceback).

        Return information about the most recent exception caught by an except
        clause in the current stack frame or in an older stack frame.

    exit(status=None, /)
        Exit the interpreter by raising SystemExit(status).

        If the status is omitted or None, it defaults to zero (i.e., success).
        If the status is an integer, it will be used as the system exit status.
        If it is another kind of object, it will be printed and the system
        exit status will be one (i.e., failure).

    get_asyncgen_hooks()
        Return the installed asynchronous generators hooks.

        This returns a namedtuple of the form (firstiter, finalizer).

    get_coroutine_origin_tracking_depth()
        Check status of origin tracking for coroutine objects in this thread.

    getallocatedblocks()
        Return the number of memory blocks currently allocated.

    getdefaultencoding()
        Return the current default encoding used by the Unicode implementation.

    getdlopenflags()
        Return the current value of the flags that are used for dlopen calls.

        The flag constants are defined in the os module.

    getfilesystemencodeerrors()
        Return the error mode used Unicode to OS filename conversion.

    getfilesystemencoding()
        Return the encoding used to convert Unicode filenames to OS filenames.

    getprofile()
        Return the profiling function set with sys.setprofile.

        See the profiler chapter in the library manual.

    getrecursionlimit()
        Return the current value of the recursion limit.

        The recursion limit is the maximum depth of the Python interpreter
        stack.  This limit prevents infinite recursion from causing an overflow
        of the C stack and crashing Python.

    getrefcount(object, /)
        Return the reference count of object.

        The count returned is generally one higher than you might expect,
        because it includes the (temporary) reference as an argument to
        getrefcount().

    getsizeof(...)
        getsizeof(object [, default]) -> int

        Return the size of object in bytes.

    getswitchinterval()
        Return the current thread switch interval; see sys.setswitchinterval().

    gettrace()
        Return the global debug tracing function set with sys.settrace.

        See the debugger chapter in the library manual.

    intern(string, /)
        ``Intern'' the given string.

        This enters the string in the (global) table of interned strings whose
        purpose is to speed up dictionary lookups. Return the string itself or
        the previously interned string object with the same value.

    is_finalizing()
        Return True if Python is exiting.

    set_asyncgen_hooks(...)
        set_asyncgen_hooks(* [, firstiter] [, finalizer])

        Set a finalizer for async generators objects.

    set_coroutine_origin_tracking_depth(depth)
        Enable or disable origin tracking for coroutine objects in this thread.

        Coroutine objects will track 'depth' frames of traceback information
        about where they came from, available in their cr_origin attribute.

        Set a depth of 0 to disable.

    setdlopenflags(flags, /)
        Set the flags used by the interpreter for dlopen calls.

        This is used, for example, when the interpreter loads extension
        modules. Among other things, this will enable a lazy resolving of
        symbols when importing a module, if called as sys.setdlopenflags(0).
        To share symbols across extension modules, call as
        sys.setdlopenflags(os.RTLD_GLOBAL).  Symbolic names for the flag
        modules can be found in the os module (RTLD_xxx constants, e.g.
        os.RTLD_LAZY).

    setprofile(...)
        setprofile(function)

        Set the profiling function.  It will be called on each function call
        and return.  See the profiler chapter in the library manual.

    setrecursionlimit(limit, /)
        Set the maximum depth of the Python interpreter stack to n.

        This limit prevents infinite recursion from causing an overflow of the C
        stack and crashing Python.  The highest possible limit is platform-
        dependent.

    setswitchinterval(interval, /)
        Set the ideal thread switching delay inside the Python interpreter.

        The actual frequency of switching threads can be lower if the
        interpreter executes long sequences of uninterruptible code
        (this is implementation-specific and workload-dependent).

        The parameter must represent the desired switching delay in seconds
        A typical value is 0.005 (5 milliseconds).

    settrace(...)
        settrace(function)

        Set the global debug tracing function.  It will be called on each
        function call.  See the debugger chapter in the library manual.

    unraisablehook(unraisable, /)
        Handle an unraisable exception.

        The unraisable argument has the following attributes:

        * exc_type: Exception type.
        * exc_value: Exception value, can be None.
        * exc_traceback: Exception traceback, can be None.
        * err_msg: Error message, can be None.
        * object: Object causing the exception, can be None.

DATA
    __stderr__ = <_io.TextIOWrapper name='<stderr>' mode='w' encoding='utf...
    __stdin__ = <_io.TextIOWrapper name='<stdin>' mode='r' encoding='utf-8...
    __stdout__ = <_io.TextIOWrapper name='<stdout>' mode='w' encoding='utf...
    abiflags = ''
    api_version = 1013
    argv = ['/home/jfasch/venv/jfasch-home/lib64/python3.9/site-packages/i...
    base_exec_prefix = '/usr'
    base_prefix = '/usr'
    builtin_module_names = ('_abc', '_ast', '_codecs', '_collections', '_f...
    byteorder = 'little'
    copyright = 'Copyright (c) 2001-2021 Python Software Foundati...ematis...
    displayhook = <ipykernel.displayhook.ZMQShellDisplayHook object>
    dont_write_bytecode = False
    exec_prefix = '/home/jfasch/venv/jfasch-home'
    executable = '/home/jfasch/venv/jfasch-home/bin/python'
    flags = sys.flags(debug=0, inspect=0, interactive=0, opt...ation=1, is...
    float_info = sys.float_info(max=1.7976931348623157e+308, max_...epsilo...
    float_repr_style = 'short'
    hash_info = sys.hash_info(width=64, modulus=2305843009213693...iphash2...
    hexversion = 50923504
    implementation = namespace(name='cpython', cache_tag='cpython-39'...xv...
    int_info = sys.int_info(bits_per_digit=30, sizeof_digit=4)
    maxsize = 9223372036854775807
    maxunicode = 1114111
    meta_path = [<class '_frozen_importlib.BuiltinImporter'>, <class '_fro...
    modules = {'IPython': <module 'IPython' from '/home/jfasch/venv/jfasch...
    path = ['/home/jfasch/work/jfasch-home/trainings/log/detail/2021-12-01...
    path_hooks = [<class 'zipimport.zipimporter'>, <function FileFinder.pa...
    path_importer_cache = {'/home/jfasch/.ipython': FileFinder('/home/jfas...
    platform = 'linux'
    platlibdir = 'lib64'
    prefix = '/home/jfasch/venv/jfasch-home'
    ps1 = 'In : '
    ps2 = '...: '
    ps3 = 'Out: '
    pycache_prefix = None
    stderr = <ipykernel.iostream.OutStream object>
    stdin = <_io.TextIOWrapper name='<stdin>' mode='r' encoding='utf-8'>
    stdout = <ipykernel.iostream.OutStream object>
    thread_info = sys.thread_info(name='pthread', lock='semaphore', versio...
    version = '3.9.7 (default, Aug 30 2021, 00:00:00) \n[GCC 11.2.1 202107...
    version_info = sys.version_info(major=3, minor=9, micro=7, releaseleve...
    warnoptions = []

FILE
    (built-in)

References¶

A variable refers to an object (an integer, with value 42 in this case)

[21]:

a = 42
id(a)

[21]:

140106795875920

Assigning variables to other variables only increments the reference count.

[22]:

b = a
id(b)

[22]:

140106795875920

Integer increment? Are integers mutable?

[23]:

c = 666
d = c

[24]:

id(c)

[24]:

140106669190640

[25]:

id(d)

[25]:

140106669190640

[26]:

c += 3

[27]:

[27]:

[28]:

[28]:

Ah: ‘+=’ creates a new object

[29]:

id(c)

[29]:

140106669191024

Compound Datatypes¶

List, Tuple¶

[30]:

l = ['one', 2, 3.0]

[31]:

type(l)

[31]:

list

[32]:

for element in l:
    print(element)

one
2
3.0

[33]:

l.append(complex(4,0))

[34]:

[34]:

['one', 2, 3.0, (4+0j)]

[35]:

l.extend([5, 6, 7])
l

[35]:

['one', 2, 3.0, (4+0j), 5, 6, 7]

[36]:

l.insert(0, None)
l

[36]:

[None, 'one', 2, 3.0, (4+0j), 5, 6, 7]

[37]:

for element in l:
    print(element)

None
one
2
3.0
(4+0j)
5
6
7

[38]:

del l[3]

[39]:

[39]:

[None, 'one', 2, (4+0j), 5, 6, 7]

[40]:

copied_l = l

[41]:

copied_l

[41]:

[None, 'one', 2, (4+0j), 5, 6, 7]

[42]:

[42]:

[None, 'one', 2, (4+0j), 5, 6, 7]

[43]:

id(l)

[43]:

140106669249856

[44]:

l.append(10000000)
l

[44]:

[None, 'one', 2, (4+0j), 5, 6, 7, 10000000]

[45]:

id(l)

[45]:

140106669249856

[46]:

id(copied_l)

[46]:

140106669249856

[47]:

copied_l

[47]:

[None, 'one', 2, (4+0j), 5, 6, 7, 10000000]

Enter Tuples …

[48]:

t = ('one', 2, 3.0)

[49]:

[49]:

('one', 2, 3.0)

[50]:

type(t)

[50]:

tuple

[51]:

copied_t = t

[52]:

try:
    t.append(10000000)
except Exception as e:
    print(type(e), e)

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

[53]:

tuple_containing_one_element = (1)
type(tuple_containing_one_element)

[53]:

int

[54]:

1 + 2 * 3

[54]:

[55]:

(1 + 2) * 3

[55]:

[56]:

tuple_containing_one_element = (1,)
type(tuple_containing_one_element)

[56]:

tuple

Sequence: ‘+’ operator

[57]:

l1 = [1,2,3]
l2 = [4,5,6]
l1 + l2

[57]:

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

[58]:

l1

[58]:

[1, 2, 3]

[59]:

l2

[59]:

[4, 5, 6]

Dictionary¶

[60]:

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

[61]:

type(trans)

[61]:

dict

[62]:

trans['three'] = 3

[63]:

trans

[63]:

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

[64]:

import pprint

[65]:

pprint.pprint(trans, width=10)

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

[66]:

trans['three']

[66]:

[67]:

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

<class 'KeyError'> 'four'

[68]:

value = trans.get('three')
if value:
    print(value)
else:
    print('na, leider nicht')

[69]:

value = trans.get('four')
if value:
    print(value)
else:
    print('na, leider nicht')

na, leider nicht

None? NoneType?

[70]:

print(value)

None

[71]:

type(value)

[71]:

NoneType

Boolean value of None?

[72]:

bool(None)

[72]:

False

[73]:

bool(5)

[73]:

True

[74]:

bool(0)

[74]:

False

[75]:

trans['zero'] = 0
pprint.pprint(trans, width=10)

{'one': 1,
 'three': 3,
 'two': 2,
 'zero': 0}

[76]:

value = trans.get('zero')
if value:    # "found"
    print(value)
else:
    print('na, leider nicht')

na, leider nicht

[77]:

value = trans.get('zero')
if value is not None:
    print(value)
else:
    print('na, leider nicht')

Remove entries

[78]:

del trans['zero']

[79]:

trans

[79]:

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

Set¶

[80]:

s = {1,2,3,4,5}
type(s)

[80]:

set

[81]:

4 in s

[81]:

True

[82]:

s.remove(4)

[83]:

4 in s

[83]:

False

[84]:

s.add(4)

[85]:

[85]:

{1, 2, 3, 4, 5}

Iteration¶

List¶

[86]:

l = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
for element in l:
    print(element)

[87]:

9 in l

[87]:

True

Tuple¶

[88]:

t = (1, 2, 3, 4, 5, 6, 7, 8, 9, 0)
for element in t:
    print(element)

Set¶

[89]:

s = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0}
for element in s:
    print(element)

Note: sets are not ordered!

[90]:

9 in s

[90]:

True

Dictionary¶

[91]:

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

[92]:

for element in d:
    print(element)

one
two
three

[93]:

'one' in d

[93]:

True

[94]:

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

1
2
3

[95]:

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

one
two
three

[96]:

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

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

Potschert: manual tuple unpacking

[97]:

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

Key: one, Value: 1
Key: two, Value: 2
Key: three, Value: 3

[98]:

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

Key: one, Value: 1
Key: two, Value: 2
Key: three, Value: 3

Tuple Unpacking: What Else¶

[99]:

l = [
    [1234, 'joerg', 55],
    [666, 'satan', 10**10],
    [42, 'queen', 10*2],
]

[100]:

for svnr, name, age in l:
    print(f'SVNr:{svnr}, Name:{name}, Age:{age}')

SVNr:1234, Name:joerg, Age:55
SVNr:666, Name:satan, Age:10000000000
SVNr:42, Name:queen, Age:20

[101]:

a, b = 1, 2

[102]:

[102]:

[103]:

[103]:

Same as:

[104]:

(a, b) = (1, 2)

Swap two variables:

[105]:

a, b = b, a

[106]:

[106]:

[107]:

[107]:

[108]:

a, b, = 1, 2,

Swap, traditional

[109]:

c = a
a = b
b = c

[110]:

[110]:

[111]:

[111]:

Function returns multiple values

[112]:

def f(a, b):
    return a+b

[113]:

f(1,2)

[113]:

[114]:

def f(a, b):
    return a+b, a-b, a*b, a/b

[115]:

sum, diff, prod, quot = f(100, 50)

[116]:

sum

[116]:

[117]:

diff

[117]:

[118]:

prod

[118]:

[119]:

quot

[119]:

2.0

Comprehensions¶

[120]:

numbers = (1, 2, 3, 4, 5, 6, 7, 8, 9)

[121]:

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

[122]:

result = squares(numbers)
result

[122]:

[1, 4, 9, 16, 25, 36, 49, 64, 81]

List comprehension

[123]:

result = [n**2 for n in numbers]
result

[123]:

[1, 4, 9, 16, 25, 36, 49, 64, 81]

[124]:

[n**2 for n in numbers if n%2==0]

[124]:

[4, 16, 36, 64]

Set comprehension

[125]:

result = {n**2 for n in numbers}
result

[125]:

{1, 4, 9, 16, 25, 36, 49, 64, 81}

Dictionary comprehension

Mapping Number->Square number

[126]:

result = {n: n**2 for n in numbers}
pprint.pprint(result, width=5)

{1: 1,
 2: 4,
 3: 9,
 4: 16,
 5: 25,
 6: 36,
 7: 49,
 8: 64,
 9: 81}

WTF? How would I use that?

[127]:

resultset = [
    [1234, 'joerg', 55],
    [666, 'satan', 10**10],
    [42, 'queen', 10*2],
]

Dictionary: SVNr -> (Name, Age)

[128]:

def resultset_to_local_db(rs):
    d = {}
    for svnr, name, age in rs:
        d[svnr] = (name, age)
    return d

[129]:

my_local_db = resultset_to_local_db(resultset)

[130]:

my_local_db

[130]:

{1234: ('joerg', 55), 666: ('satan', 10000000000), 42: ('queen', 20)}

Potschert!!

[131]:

my_local_db = {svnr: (name, age) for svnr, name, age in resultset}
my_local_db

[131]:

{1234: ('joerg', 55), 666: ('satan', 10000000000), 42: ('queen', 20)}

`os.path`¶

[132]:

import os.path

[133]:

filename = '/home/jfasch/tmp/2021-12-01/tests/__init__.py'

Directory Name?

[134]:

dirname = os.path.dirname(filename)
dirname

[134]:

'/home/jfasch/tmp/2021-12-01/tests'

[135]:

os.path.basename(filename)

[135]:

'__init__.py'

[136]:

path = os.path.join(dirname, '../src')
path

[136]:

'/home/jfasch/tmp/2021-12-01/tests/../src'

[137]:

normalized_path = os.path.normpath(path)
normalized_path

[137]:

'/home/jfasch/tmp/2021-12-01/src'

[138]:

import os

[139]:

os.sep     # Doze: '\\' (r'\'))

[139]:

'/'

[140]:

os.path.join('..', 'src')

[140]:

'../src'

[141]:

os.path.split(normalized_path)

[141]:

('/home/jfasch/tmp/2021-12-01', 'src')

Iterable¶

[142]:

s = 'abc'
for element in s:
    print(element)

a
b
c

[143]:

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

``range()``

[144]:

l = []
i = 0
while i < 1000:
    l.append(i)
    i += 1

[145]:

[145]:

STUPID!

[146]:

r = range(3)
for element in r:
    print(element)

0
1
2

Iterator Protocol¶

A list is iterable

[147]:

l = [3, 4, 5]
iterator = iter(l)

[148]:

element = next(iterator)
element

[148]:

[149]:

element = next(iterator)
element

[149]:

[150]:

element = next(iterator)
element

[150]:

[151]:

try:
    element = next(iterator)
except Exception as e:
    print(type(e), e)

<class 'StopIteration'>

A ``range`` object is iterable

[152]:

r = range(3)
for element in r:
    print(element)

0
1
2

[153]:

for element in range(3, 6):
    print(element)

3
4
5

[154]:

for element in range(4, 20, 2):
    print(element)

[155]:

timeaxis = range(1000)
iterator = iter(timeaxis)

[156]:

next(iterator)

[156]:

[157]:

while True:
    try:
        print(next(iterator))
    except StopIteration:
        break

`yield`¶

A naive function:

[158]:

def myrange(begin, end, step):
    l = []
    element = begin
    while element < end:
        l.append(element)
        element += step
    return l

[159]:

for element in myrange(4, 20, 2):
    print(element)

[160]:

for element in myrange(4, 20000, 2):
    print(element)

STUPID!

A far less naive generator:

[161]:

def myrange(begin, end, step):
    element = begin
    while element < end:
        yield element
        element += step

[162]:

for element in myrange(4, 20000, 2):
    print(element)

[163]:

g = myrange(4, 20000, 2)
type(g)

[163]:

generator

JSON¶

[164]:

import json

Send away

[165]:

l_to_send = [1, 2, 3, 4]
json_to_send = json.dumps(l_to_send)
json_to_send

[165]:

'[1, 2, 3, 4]'

[166]:

type(json_to_send)

[166]:

str

Receive

[167]:

json_received = json_to_send

[168]:

l_received = json.loads(json_received)
l_received

[168]:

[1, 2, 3, 4]

More datatypes?

[169]:

d = {
    'one': 1,
    'two': 2,
}
json.dumps(d)

[169]:

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

[170]:

l = [
    ('hugo', 10, 1, 2, 3),
    ('sine', 11, 0, 0, 0),
]
serialized = json.dumps(l)
serialized

[170]:

'[["hugo", 10, 1, 2, 3], ["sine", 11, 0, 0, 0]]'

[171]:

json.loads(serialized)

[171]:

[['hugo', 10, 1, 2, 3], ['sine', 11, 0, 0, 0]]

Everything is an Object of a Type¶

[172]:

i = 666

[173]:

j = i

[174]:

id(i)

[174]:

140106668681968

[175]:

id(j)

[175]:

140106668681968

[176]:

class X:
    def __init__(self, blah):
        self.blah = blah

[177]:

x = X('hallo')

[178]:

x.blah

[178]:

'hallo'

[179]:

type(X)

[179]:

type

[180]:

print(X)

<class '__main__.X'>

[181]:

Y = X

[182]:

print(type(Y))

<class 'type'>

[183]:

Y is X

[183]:

True

[184]:

isinstance(x, X)

[184]:

True

[185]:

isinstance(x, Y)

[185]:

True

[186]:

def f():
    print('calling f')

[187]:

type(f)

[187]:

function

[188]:

type(type(f))

[188]:

type

[189]:

f()

calling f

[190]:

g = f
g()

calling f

Generators, used more creatively¶

Generating wall clock time, aka iterating over wall clock timestamps

[206]:

timeaxis = range(10)
for timestamp in timeaxis:
    print(timestamp)

Hm, and real timestamps, iterated likewise?

[207]:

import time
def wallclock_axis():
    while True:
        yield time.time()

[210]:

i = 0
for ts in wallclock_axis():
    if i < 10:
        print(ts)
        i += 1
        time.sleep(0.1)
    else:
        break

1638538131.1975703
1638538131.2978473
1638538131.3981225
1638538131.498449
1638538131.5987027
1638538131.698947
1638538131.7996597
1638538131.899947
1638538132.0001943
1638538132.1010473

Exception Handling and Exception Types¶

[216]:

issubclass(TypeError, Exception)

[216]:

True

[217]:

def f(name):
    pass

[220]:

try:
    f()
except Exception:
    print('bummer')

bummer

[222]:

try:
    f()
except TypeError:
    print('bummer, type error')

bummer, type error

Order of except clauses is relevant:

[226]:

try:
    f()
except Exception as e:
    print('bummer, but no further information', type(e))
except TypeError as e:
    print('bummer, maybe name parameter missing', type(e))

bummer, but no further information <class 'TypeError'>

[228]:

try:
    f()
except TypeError as e:
    print('bummer, maybe name parameter missing', type(e))
except Exception as e:
    print('bummer, but no further information', type(e))

bummer, maybe name parameter missing <class 'TypeError'>

2021-12-17¶

Shift Operators¶

[1]:

number = 0b10110
number

[1]:

[8]:

hex(number)

[8]:

'0x16'

[9]:

1*16**1 + 6*16**0

[9]:

[10]:

bin(number)

[10]:

'0b10110'

[11]:

1*2**4 + 0*2**3 + 1*2**2 + 1*2**1 + 0*2**0

[11]:

[12]:

number >> 1

[12]:

[13]:

bin(number>>1)

[13]:

'0b1011'

[15]:

bin(number)

[15]:

'0b10110'

Hardware Register: set bit #3 to high

[23]:

bit_3 = 0b00001
bin(bit_3)

[23]:

'0b1'

[24]:

bit_3 = 0b00001 << 3

[26]:

bin(bit_3)

[26]:

'0b1000'

[27]:

bin(number)

[27]:

'0b10110'

[28]:

new_number = number | bit_3
bin(new_number)

[28]:

'0b11110'

Bitwise Operators

[29]:

num1 = 0b110101101
num2 = 0b101110100

[31]:

bin(num1 & num2)

[31]:

'0b100100100'

[35]:

bin(num1 | num2)

[35]:

'0b111111101'

[36]:

num = 0b1010
num <<= 1
bin(num)

[36]:

'0b10100'

PCAP Sample Exam¶

Question 1

[37]:

2 ** 3 ** 2 ** 1

[37]:

Operator Precedence

[38]:

2 + 3 * 4

[38]:

[39]:

2 + (3 * 4)

[39]:

[40]:

(2 + 3) * 4

[40]:

[41]:

2 * 3 * 4

[41]:

[42]:

2 * (3 * 4)

[42]:

[43]:

2 ** 3 ** 2 ** 1

[43]:

[45]:

((2 ** 3) ** 2) ** 1

[45]:

[46]:

2 ** (3 ** (2 ** 1))

[46]:

Question 3

Floor division ``//``

[48]:

3/2

[48]:

1.5

[49]:

3//2

[49]:

Question 4

[50]:

print(1, 2)

1 2

[51]:

print(1, 2, sep=',')

1,2

[52]:

print(1)

[53]:

print(1, end='***')

1***

[54]:

print(1, 2)
print(2, 3)

1 2
2 3

[55]:

print(1, 2, sep=',')
print(2, 3, sep=',')

1,2
2,3

[56]:

print(1, 2, sep='\n')
print(2, 3, sep='\n')

[59]:

print(1, 2, sep=',', end='***')
print(2, 3, sep=';', end='+++')

1,2***2;3+++

[63]:

n = 0
while n < 4:
    n += 1
    print(n, end=' ')

1 2 3 4

[64]:

print(1, 2, 3, 4, sep='fuzzi', end='********')

1fuzzi2fuzzi3fuzzi4********

[65]:

print(1, 2, 3, 4, sep='fuzzi', end='********', file=open('mei-super-file', 'w'))

[67]:

open('mei-super-file').read()

[67]:

'1fuzzi2fuzzi3fuzzi4********'

Question 5

[68]:

x = 0
y = 2

[69]:

z = len("Python")
z

[69]:

[71]:

x = y > z

[72]:

print(x)

False

[74]:

print(type(x))

<class 'bool'>

Question 6

Binary Operators: Exclusive OR

[29]:

num1 = 0b110101101
num2 = 0b101110100

[77]:

bin(num1 ^ num2)

[77]:

'0b11011001'

Question 11

Slicing

[94]:

l = [1, 2, 3, 'a', 'b', 'c', 6, 7, 8]

[95]:

l[2]

[95]:

[96]:

l[5]

[96]:

'c'

[97]:

l[2:5]

[97]:

[3, 'a', 'b']

[98]:

l[2:5:2]

[98]:

[3, 'b']

[99]:

s = 'abcdef'
s[2:5]

[99]:

'cde'

Immutable, Slice Assignment

[100]:

[100]:

[1, 2, 3, 'a', 'b', 'c', 6, 7, 8]

[102]:

l[3:6] = [4, 5]

[103]:

[103]:

[1, 2, 3, 4, 5, 6, 7, 8]

[104]:

[104]:

'abcdef'

Strings are immutable, which means that there is no slice assignment. Slicing is possible though!!

[106]:

try:
    s[2:4] = ['x', 'y']
except Exception as e:
    print(type(e), e)

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

Question 12

[110]:

1 > 2     # numerical comparison

[110]:

False

[111]:

'a' > 'b'    # lexical comparison

[111]:

False

[113]:

'1' > '2'    # lexical comparison

[113]:

False

[115]:

'abc' > 'def'

[115]:

False

[117]:

x = '20'
y = '30'
x > y

[117]:

False

[119]:

x = '020'
x > y

[119]:

False

[121]:

x = '200'
y = '30'
x > y

[121]:

False

[122]:

'2' > '3'

[122]:

False

[123]:

int('200') > int('30')

[123]:

True

Question 13

[125]:

name = 'Faschingbauer'
name[12]

[125]:

'r'

[127]:

try:
    name[13]
except Exception as e:
    print(type(e), e)

<class 'IndexError'> string index out of range

[129]:

name[-1]

[129]:

'r'

[130]:

name[-4]

[130]:

'a'

[131]:

name[-4:13]

[131]:

'auer'

[132]:

name[-4:12]

[132]:

'aue'

Question 15

Dictionary iteration

[134]:

dict = { 'a': 1, 'b': 2, 'c': 3 }

[136]:

for elem in dict:
    print(elem)

a
b
c

[138]:

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

a
b
c

[140]:

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

1
2
3

[142]:

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

('a', 1)
('b', 2)
('c', 3)

[145]:

for k, v in dict.items():      # tuple unpacking
    print(k, v)

a 1
b 2
c 3

Tuple unpacking

[146]:

t = ('a', 1)

[147]:

t2 = t
t2

[147]:

('a', 1)

[148]:

k = t[0]
v = t[1]
print(k, v)

a 1

[149]:

k, v = t     # tuple unpacking
print(k, v)

a 1

Question 17

List comprehension

[150]:

l = [0, 1, 2, 3, 4]
squares = [elem**2 for elem in l]
squares

[150]:

[0, 1, 4, 9, 16]

[152]:

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

[152]:

[0, 1, 4, 9, 16]

[153]:

[elem**2 for elem in l]

[153]:

[0, 1, 4, 9, 16]

Dictionary comprehension

[156]:

{elem: elem**2 for elem in l}

[156]:

{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

Set comprehension

[158]:

{elem**2 for elem in l}

[158]:

{0, 1, 4, 9, 16}

[161]:

try:
    lst = [i // i for i in range(0,4)]
    print(lst)
except Exception as e:
    print(type(e), e)

<class 'ZeroDivisionError'> integer division or modulo by zero

[163]:

for i in range(0,4):
    print(i)

[165]:

try:
    0/0
except Exception as e:
    print(type(e), e)

<class 'ZeroDivisionError'> division by zero

[167]:

try:
    0//0
except Exception as e:
    print(type(e), e)

<class 'ZeroDivisionError'> integer division or modulo by zero

Question 18

[168]:

lst = [[c for c in range(r)] for r in range(3)]
lst

[168]:

[[], [0], [0, 1]]

Question 20

[170]:

lst1 = "12,34"
lst1.split(',')

[170]:

['12', '34']

[173]:

lst2 = lst1.split(',')

Question 22

[174]:

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

[176]:

[elem**2 for elem in l]

[176]:

[0, 1, 4, 9, 16]

[178]:

for elem in l:
    print(elem**2)

[180]:

def f(n):
    return n**2
for elem in l:
    print(f(elem))

[183]:

f = lambda n: n**2
for elem in l:
    print(f(elem))

[184]:

for elem in l:
    print((lambda n: n**2)(elem))

Question 23

[185]:

import math

[186]:

print(math.pi)

3.141592653589793

[187]:

from math import pi
print(pi)

3.141592653589793

[188]:

from math import pi as joerg
print(joerg)

3.141592653589793

System Errors¶

[3]:

try:
    f = open('/xyz/abc')
except Exception as e:
    print(type(e), e)
    print(e.errno)

<class 'FileNotFoundError'> [Errno 2] No such file or directory: '/xyz/abc'
2

[4]:

from os import strerror

[6]:

strerror(2)

[6]:

'No such file or directory'

[8]:

try:
    open('/etc/passwd', 'w')
except Exception as e:
    print(type(e), e)

<class 'PermissionError'> [Errno 13] Permission denied: '/etc/passwd'

[9]:

strerror(13)

[9]:

'Permission denied'

Notebook¶

More About Strings¶

References¶

Compound Datatypes¶

List, Tuple¶

Dictionary¶

Set¶

Iteration¶

List¶

Tuple¶

Set¶

Dictionary¶

Tuple Unpacking: What Else¶

Comprehensions¶

os.path¶

Iterable¶

Iterator Protocol¶

yield¶

JSON¶

Everything is an Object of a Type¶

Generators, used more creatively¶

Exception Handling and Exception Types¶

2021-12-17¶

Shift Operators¶

PCAP Sample Exam¶

System Errors¶

`os.path`¶

`yield`¶