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| Beide Seiten, vorherige Überarbeitung Vorherige Überarbeitung Nächste Überarbeitung | Vorherige Überarbeitung | ||
| talit:python_basics [2020-02-09 21:38] – sca | talit:python_basics [2020-02-09 21:42] (aktuell) – sca | ||
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| </ | </ | ||
| - | Note that you can also write a number as a string, e.g., `{s = ' | + | Note that you can also write a number as a string, e.g., `s = ' |
| However, `s` will be treated as text and not as a number, therefore, you cannot do any calculations with it. | However, `s` will be treated as text and not as a number, therefore, you cannot do any calculations with it. | ||
| Also, you can use variables with more than one character, e.g., `mystring = "Hello World" | Also, you can use variables with more than one character, e.g., `mystring = "Hello World" | ||
| Zeile 93: | Zeile 93: | ||
| 1. Can you use numbers or special characters like `?, | 1. Can you use numbers or special characters like `?, | ||
| - | <!-- You can even use numbers in variable names, as long as they are not in the beginning, e.g., `mystring13 = "Hello World" | ||
| - | But you can NOT use special characters in variable names | ||
| - | --> | ||
| 2. How can you add a line break to a string? | 2. How can you add a line break to a string? | ||
| - | <!-- % mystring = " | ||
| 3. Is Python case-sensitive? | 3. Is Python case-sensitive? | ||
| 4. Given a (long enough) string `s`, what do the commands | 4. Given a (long enough) string `s`, what do the commands | ||
| Zeile 106: | Zeile 102: | ||
| ## Integers & floats | ## Integers & floats | ||
| - | \label{sec integers and floats} | ||
| Next, let's have a look at numbers, in particular integers and floats. | Next, let's have a look at numbers, in particular integers and floats. | ||
| Zeile 295: | Zeile 290: | ||
| - | # Conditions | + | # Conditions & Booleans |
| We can check if one or multiple conditions are satisfied. | We can check if one or multiple conditions are satisfied. | ||
| Zeile 346: | Zeile 341: | ||
| # If statements | # If statements | ||
| - | In an `if' | + | In an `if` statement, the action depends on conditions. |
| Let's say we are given some number $a$ and want to determine its absolute value. It is given by $a$ if $a \geq 0$ and by $-a$ if $a < 0$. | Let's say we are given some number $a$ and want to determine its absolute value. It is given by $a$ if $a \geq 0$ and by $-a$ if $a < 0$. | ||
| We can realize this by | We can realize this by | ||
| Zeile 359: | Zeile 354: | ||
| In the first line, we just choose some number. | In the first line, we just choose some number. | ||
| Feel free to play around with its value. | Feel free to play around with its value. | ||
| - | In line 3, the `if' | + | In line 3, the `if` statement begins. |
| It starts with `if` and is followed by a condition, here `a < 0`, and a mandatory colon. | It starts with `if` and is followed by a condition, here `a < 0`, and a mandatory colon. | ||
| If the condition is `True` (satisfied), | If the condition is `True` (satisfied), | ||
| Zeile 414: | Zeile 409: | ||
| Second, we discuss the **while-loop**. It repeats a piece of code as long as a condition is satisfied. | Second, we discuss the **while-loop**. It repeats a piece of code as long as a condition is satisfied. | ||
| - | Careful: If you have a bug in your code and the condition is always true, you have an `infinite loop': the code will never stop running and you will have to kill the process manually. | + | Careful: If you have a bug in your code and the condition is always true, you have an **infinite loop**: the code will never stop running and you will have to kill the process manually. |
| A simple example of a while-loop is: | A simple example of a while-loop is: | ||
| Zeile 441: | Zeile 436: | ||
| There are many additional packages that can be imported. | There are many additional packages that can be imported. | ||
| - | For doing math, `numpy' | + | For doing math, `numpy` is particular useful. |
| For example, it contains a lot of predefined functions like trigonometric functions. | For example, it contains a lot of predefined functions like trigonometric functions. | ||
| Let us do an example | Let us do an example | ||
| Zeile 450: | Zeile 445: | ||
| print(np.pi) | print(np.pi) | ||
| </ | </ | ||
| - | In the first line, we import the `numpy' | + | In the first line, we import the `numpy` package and give it the short name `np`. Of course, you could use a different name than `np` but this is the common choice. |
| - | Each time we call a function (or something else) from numpy, we have to start with `np.', in order for Python to know that it has to look inside the numpy package. This is exactly what we do on line 3: We call the sine function defined in numpy and evaluate it for the argument $2$. In the last line, we print the value of the constant $\pi$. | + | Each time we call a function (or something else) from numpy, we have to start with `np.`, in order for Python to know that it has to look inside the numpy package. This is exactly what we do on line 3: We call the sine function defined in numpy and evaluate it for the argument $2$. In the last line, we print the value of the constant $\pi$. |
| **Questions: | **Questions: | ||
| Zeile 463: | Zeile 458: | ||
| # Elapsed time | # Elapsed time | ||
| - | \label{sec elapsed time} | ||
| If you want to test the efficiency of your code, it is useful to measure the time needed for the calculation: | If you want to test the efficiency of your code, it is useful to measure the time needed for the calculation: | ||
sca