Programmieren lernen mit Python

1. 00:00Welcome to the next lesson.
2. 00:03In this one we want to deal with variables.
3. 00:06First of all, introduce yourselves, that you have a box.
4. 00:09In this box we can now pack for example a T-shirt and label them with the name clothing.
5. 00:15Now, when we open the box of clothes, is in this one the T-shirt.
6. 00:19But we can also take the T-shirt out of the box and put some pants in instead.
7. 00:25Now if we reopen the box of clothes, the T-shirt is no longer in this one, but the pants.
8. 00:30Let us look at the same example again in Python:
9. 00:33We got our box back. and want to put the T-shirt inside first.
10. 00:38So in Python we write clothing, then an is-equal, and then the text "T-shirt".
11. 00:44We are talking about assignment in this is-alike.
12. 00:48So first we have the variable name, that is, the labeling of the box, then the assignment of the
13. 00:54and then the contents of the box. that is, here the value with the text "T-shirt".
14. 00:59Just like in the box, we can take the T-shirt out and can put some pants in instead.
15. 01:05In Python we write about it clothing is-equal and then again the text "pants."
16. 01:10What is important is that we as well as in the box replace the contents.
17. 01:16That means we take the T-shirt out and will not be able to access them in the further course of Python, so we overwrote it.
18. 01:24But we can not only set variables in Python, but also read the value of this variable quite simply.
19. 01:32For example, if we want to output the text "T-shirt", we can simply write print "T-shirt" and receive the desired edition.
20. 01:40Another possibility is, however, our previously defined variable kleidung, to which we have assigned the value "T-shirt".
21. 01:48So we can then write: print clothing, that is, we pass the variable kleidung to the function print.
22. 01:56If we now execute the whole thing, the variable name kleidung is replaced by the value of this variable, i.e. the text "T-Shirt", and we're holding the "T-shirt" issue.
23. 02:08It is important that you do not write clothing in quotation marks, because otherwise the program will think that it is a text and not the name of the variable.
24. 02:17Also, once we use it, the variable is is not consumed, but can still be used.
25. 02:25We can use a variable, for example, to create a second variable.
26. 02:31First, the same example again:
27. 02:33So we have the variable clothing with the value "T-shirt" as in line 1.
28. 02:38In line 2 we then create a second variable, so a second garment, which we also assign to the value "T-shirt".
29. 02:48For this we write: second_clothing = and then the name of the first variable clothing.
30. 02:55So we first read the content of the variable kleidung and assign this content to the second variable named second_clothing.
31. 03:05So we make a copy.
32. 03:08In the third line we can then output this value and receive the T-shirt as an edition as desired.
33. 03:15On the other hand, if we try to use a variable, to which we have not previously assigned a value, we get an error.
34. 03:23You can imagine the whole thing like this like you're looking for a box with that name, but it doesn't exist.
35. 03:29Python then gives us a NameError, a so-called name mistake.
36. 03:33This means that we have tried to use a variable, to which we have previously assigned no value at all.
37. 03:40There are a few rules to be observed when naming variables:
38. 03:46Variables should always be written in lower case and without spaces, that is, instead of a space, simply use an underscore.
39. 03:54This way you can still get an overview of a variable name as we have illustrated here by way of example.
40. 04:01And please do not use umlauts like ä, ö or ü and also no special characters.
41. 04:07It is also important to know that for variable names in Python upper and lower case is crucial.
42. 04:15That is, the three examples of variable names, which you see here on the slide, all describe different variables.
43. 04:21We will always use the first option, since this is the standard in Python, so to speak.
44. 04:27It is also helpful to name the variables as meaningful as possible, so that you still know, especially in longer programs, in which variable you have stored which value.
45. 04:38In this video we have shown you variables.
46. 04:42These are used to store individual values in Python under a freely selectable name and retrieve it later.
47. 04:51To create a variable, we write the variable name then Is-Equal and then the value such as the text "T-Shirt", which we have used several times.
48. 05:00And you can change the content of a variable at any time and assign a new value.

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