TEST-DRIVES: USING IPYTHON AND JUPYTER NOTEBOOKS
In this section, you’ll testdrive the IPython interpreter in two modes:
Before reading this section, follow the instructions in the Before You Begin section to install the Anaconda Python distribution, which contains the IPython interpreter.
- In interactive mode, you’ll enter small bits of Python code called snippets and immediately see their results.
- In script mode, you’ll execute code loaded from a file that has the .py extension (short for Python). Such files are called scripts or programs, and they’re generally longer than the code snippets you’ll use in interactive mode.
Then, you’ll learn how to use the browserbased environment known as the Jupyter Notebook for writing and executing Python code.
Jupyter supports many programming languages by installing their “kernels.” For more information see https://github.com/jupyter/jupyter/wiki/Jupyter-kernels.
Using IPython Interactive Mode as a Calculator
Let’s use IPython interactive mode to evaluate simple arithmetic expressions.
Entering IPython in Interactive Mode
First, open a commandline window on your system:
- On macOS, open a Terminal from the Applications folder’s Utilities subfolder.
- On Windows, open the Anaconda Command Prompt from the start menu.
- On Linux, open your system’s Terminal or shell (this varies by Linux distribution).
In the commandline window, type ipython, then press Enter (or Return). You’ll see text like the following, this varies by platform and by IPython version:
Click here to view code image
Python 3.7.0 | packaged by JuTT BaDshaH | (default, Dec 10, 2020, 13:11:52)
Type 'copyright', 'credits' or 'license' for more information
IPython 6.5.0 An enhanced Interactive Python. Type '?'
for help.
In [1]:
The text "In [1]:" is a prompt, indicating that IPython is waiting for your input. You can type ? for help or begin entering snippets, as you’ll do momentarily.
Evaluating Expressions
In interactive mode, you can evaluate expressions:
In [1]: 45 + 72
Out[1]: 117
In [2]:
After you type 45 + 72 and press Enter, IPython reads the snippet, evaluates it and prints its result in Out[1]. Then IPython displays the In [2] prompt to show that it’s waiting for you to enter your second snippet. For each new snippet, IPython adds 1 to the number in the square brackets. Each In [1] prompt in the article indicates that we’ve started a new interactive session. We generally do that for each new section of a chapter.
Let’s evaluate a more complex expression:
Click here to view code image
In [2]: 5 * (12.7 4) / 2
Out[2]: 21.75
Python uses the asterisk (*) for multiplication and the forward slash (/) for division. As in mathematics, parentheses force the evaluation order, so the parenthesized expression (12.7-4) evaluates first, giving 8.7. Next, 5 * 8.7 evaluates giving 43.5. Then, 43.5 / 2 evaluates, giving the result 21.75, which IPython displays in Out[2]. Whole numbers, like 5, 4 and 2, are called integers. Numbers with decimal points, like 12.7, 43.5 and 21.75, are called floatingpoint numbers.
Exiting Interactive Mode
To leave interactive mode, you can:
- Type the exit command at the current In [] prompt and press Enter to exit immediately.
- Type the key sequence <Ctrl> + d (or <control> + d). This displays the prompt "Do you really want to exit ([y]/n)?". The square brackets around y indicate that it’s the default response—pressing Enter submits the default response and exits.
- Type <Ctrl> + d (or <control> + d) twice (macOS and Linux only).
Executing a Python Program Using the IPython Interpreter
In this section, you’ll execute a script named RollDieDynamic.py that you’ll write in Chapter 6. The .py extension indicates that the file contains Python source code. The script RollDieDynamic.py simulates rolling a sixsided die. It presents a colorful animated visualization that dynamically graphs the frequencies of each die face.
Changing to This Chapter’s Examples Folder
You’ll find the script in the article’s ch01 sourcecode folder. In the Before You Begin section you extracted the examples folder to your user account’s Documents folder. Each chapter has a folder containing that chapter’s source code. The folder is named ch##, where ## is a two-digit chapter number from 01 to 17. First, open your system’s command-line window. Next, use the cd (“change directory”) command to change to the ch01 folder:
- On macOS/Linux, type cd ~/Documents/examples/ch01, then press Enter.
- On Windows, type cd C:\Users\YourAccount\Documents\examples\ch01, then press Enter.
Executing the Script
To execute the script, type the following command at the command line, then press Enter:
ipython RollDieDynamic.py 6000 1
The script displays a window, showing the visualization. The numbers 6000 and 1 tell this script the number of times to roll dice and how many dice to roll each time. In this case, we’ll update the chart 6000 times for 1 die at a time.
For a sixsided die, the values 1 through 6 should each occur with “equal likelihood”—the probability of each is 1/6 or about 16.667%. If we roll a die 6000 times, we’d expect about 1000 of each face. Like coin tossing, die rolling is random, so there could be some faces with fewer than 1000, some with 1000 and some with more than 1000. We took the screen captures below during the script’s execution. This script uses randomly generated die values, so your results will differ. Experiment with the script by changing the value 1 to 100, 1000 and 10000. Notice that as the number of die rolls gets larger, the frequencies zero in on 16.667%. This is a phenomenon of the “Law of Large Numbers.”
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| BY JuTT BaDshaH |
Creating Scripts
Problems That May Occur at Execution Time