= Treffen vom 10. 07. 2019 =

 * [[https://www.meetup.com/PYUGAT/events/262253008/|Meetup-Seite zu diesem Treffen]]

== Agenda ==
 * Begrüßung
 * Metalab
 * Vorstellungsrunde
 * [[FrontPage|Wiki]], MailingLists, [[https://twitter.com/pyugat|Twitter]], [[http://www.meetup.com/PYUGAT/|Meetup]], [[http://webchat.freenode.net/?channels=#pyugat|IRC: #pyugat on freenode]], [[https://flattr.com/thing/1804445/Python-User-Group-Austria|Flattr]]
 * Am Wiki anmelden & [[CategoryHomepage|persönliche Seite]] anlegen (Kontaktinfos, Name, Interessen, Foto,…)
 * Hands-on in Python:

{{{#!highlight python
>>> seq = [1,2,3,4,5,6,7]
>>> val1, *_, num2, num3 = seq
>>> _
[2, 3, 4, 5]
>>> val1
1
>>> num2
6
>>> num3
7

>>> 3 + 6
9
>>> _
9
# What does _ stand for?

>>> import math
>>> math.sin
<built-in function sin>
>>> _
<built-in function sin>
>>> _(5)
-0.9589242746631385
>>> _(5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'float' object is not callable
>>> -0.9589242746631385(5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'float' object is not callable
>>> _
-0.9589242746631385
>>> _ * 2
-1.917848549326277
>>> _ * 2
-3.835697098652554
>>> _ * 2
-7.671394197305108
>>> _ * 2
-15.342788394610215
>>> _ * 2
-30.68557678922043
>>> _ * 2
-61.37115357844086
>>> _ * 2
-122.74230715688172
>>> _
-122.74230715688172
>>> _ = 42
>>> 3 * 9
27
>>> _
42
>>> del _
>>> _
42
>>> 3 * 9
27
>>> _
27

>>> math.sin(2*math.pi)
-2.4492935982947064e-16
>>> math.isclose(math.sin(2*math.pi), 0)
False
>>> math.isclose(math.sin(2*math.pi), 0, 0.0000001)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Function takes at most 2 positional arguments (3 given)
>>> math.isclose(math.sin(2*math.pi), 0.000001)
False
>>> math.isclose(math.sin(2*math.pi), -0.000001)
False
>>> math.isclose(math.sin(2*math.pi), 1)
False
>>> math.sin(0)
0.0
>>> math.sin(math.pi)
1.2246467991473532e-16
>>> math.sin(math.pi*2)
-2.4492935982947064e-16
# is math.sin(2*math.pi) close to zero? Lack of definition what is interpreted as close....

>>> def print_x_is_4():
...     x = 4
...     print(x)
... 
>>> x = 3
>>> x
3
>>> print_x_is_4()
4

>>> def print_x():
...     print(x)
... 
>>> print_x()
3

>>> def print_x_plus_x():
...     x += x
...     print(x)
... 
>>> print_x_plus_x()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in print_x_plus_x
UnboundLocalError: local variable 'x' referenced before assignment
>>> ergebnis = x + x
>>> x = ergebnis
>>> x
6
# x is defined in local scope

>>> def print_local_scope():
...     x = 4
...     x += x
...     print(x)
... 
>>> print_local_scope()
8
>>> x
6
# operation in local scope has no effect to global scope

>>> def print_global_x():
...     global x
...     x += x
...     print(x)
... 
>>> x
6
>>> print_global_x()
12
>>> x
12
# x is defined in global scope out of the function

>>> def draussen():
...     x = 8
...     def drinnen():
...         nonlocal x
...         x += x
...         print("drinnen:", x)
...     print("vorher:", x)
...     drinnen()
...     print("nachher:", x)
... 
>>> draussen()
vorher: 8
drinnen: 16
nachher: 16
>>> x
12
>>> drinnen()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'drinnen' is not defined
# function drinnen() only exists in the function draussen()
}}}

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CategoryShownotes