Programming in Python

Our learning about computing, and Python in particular, is done in a data science context. That is, the problems and projects are oriented around the use of computing to answer questions about data representing the real world. Earlier coursework has given you a chance to develop the programming skills to compute quantitative measures and visualizations in BlockPy. Learning about Python will transfer and enlarge those skills to a text-based language.

Jupyter Notebooks is a programming environment that is especially useful for creating data science reports. A Jupyter Notebook contains formatted descriptive text and images, Python code, and the output produced when this code is run. Interestingly, the descriptive text and the Python code can be interleaved, allowing the report to document both describe the results but also show how those results were computed. In coming problems the formatted text will be used to state the problem and provide an outline for the code that you will develop. In coming projects the formatted text will describe the data being analyzed, the questions to be answered about this data, and possible limitations on the answers. The Python code and its output provide the basis for answering the questions. Additional formatted text can describe the output, answer the questions, and reflect on the social impact of the answers.

We will learn about Jupyter Notebooks in two stages:

using existing notebooks, and
creating new notebooks.

Each classwork and homework problem is given in a Jupyter Notebook. To do these problems it is necessary to know how to use the given notebook to create your answer. For the class projects it is necessary to know how to create a new notebook that is appropriate for your project. Below is information to use a notebook. Additional information will be given later (in the project descriptions) about how to create a new notebook.

Using a Jupyter Notebook

Finding the Notebooks

Jupyter Notebooks are accessed using your browser (e.g., Chrome, Safari, Firefox). The notebooks for the class are at: https://jupyter1014.cs.vt.edu. This URL is the location of the server that manages the notebooks. The first thing to do is click on the "My Server" button to start the server running.

The Jupyter server will display a set of folders, one for each day of the class. For example, the folder "Day 14" contains all of the notebooks for the classwork and homework on Day 14 of the class. This is shown in the left part of the figure below. Clicking on one of these folders displays the individual notebooks for that day. For example, clicking on the "Day 14" folder displays the list of notebooks shown on the right part of the figure below. The first notebook has the name

 d14-cw3.ipynb

which stands for the day 14 (d14), classwork 3 (cw3), notebook (.ipynb). Clicking on a notebook opens the notebook in the browser. An example of this notebook is shown in the next section. The suffix .ipynb indicates that it is a Python (py) Notebook (nb).

Editing a Notebook

A Jupyter Notebook contains a sequence of "cells" arranged from top to bottom. Each cell is of one of two kinds:

a Code cell containing Python code, or
a Markdown cell containing text and images.

A notebook can contain many cells of either kind, the cells can be arrange in whatever order they are needed, and each cell can contain as much or as little content as desired.

In using the notebooks for the classwork and homework problems:

only code cells will be edited,
the number and order of cells is fixed and should not be changed.

The figure below shows a notebook used for one of the class problems. This notebook contains three code cells. Notice that a code cell has:

light a grey background color,
a number for each line of text.

The lines within each code cell are numbered separately beginning at 1.

To edit a code cell, click within the cell. The cell currently selected for editing will be highlighted by the surrounding border. In the below example, the middle code cell is the one currently selected for editing. The location of the cursor in the cell is where editing operations will occur.

The code cells will typically contain a Python comment indicating what part of the solutions code should be placed in that cell. A Python comment begins with a hash-tag (#) and extends to the end of the current line of text. In the above figure, notice that each code cell contains a Python comment on line 1 of that cell. The Python comment in the currently highlighted cell reads:

# Put here the computation that produces the desired result(s)

This means that the iteration and decision statements to compute a quantitative measure or create a list to be visualized would be placed in this cell. This usage is emphasized by the text heading Processing that precedes the code cell. In this example, the first code cell should contain the code to initialize variables and the third code cell should contain the code to generate the required output, either text from a print statement or a visualization.

Running a Notebook

One of the two controls at the top of the notebook is a "Run all" button. Clicking this button will run, or execute, the code in the notebook. The "all" in "Run all" indicates that all of the code cells are run, in order from top to bottom.

Mistakes and Feedback

If there are mistakes in the Python code there are two ways in which the mistake will be reported. In the figure below the wrong syntax has been used to initialize a variable to zero. The word "set" was a label on a BlockPy block that can be used for initialization, but the word "set" does not make sense in this context in Python. When mistakes like this are detected a message is displayed in the notebook immediately below the cell containing the mistake. The message in the figure below notes the place where the mistake occurred and describes the mistake. The language used in these messages is defined by the notebook and may be difficult to understand.

The second way in which mistakes are reported is by a message displayed in the notebook below the label "Feedback" at the bottom of the notebook. These messages have been developed specifically for this course and should be readable and meaningful. Be sure to check for this feedback and resolve the mistakes indicated by the feedback. The mistake described by the feedback message may in any of the code cells, not just the immediately preceding code cell. The location of where the feedback messages appear is shown in the next figure.

Output

The output is generated by a code cell is displayed in the notebook immediately below the code cell. The output may be either the text generated by a print statement or a visualization generated by plotting commands. The figure below shows text output from a print statement on the upper-left and a histogram generated by plotting statements on the lower-right.

Notebook Grading

Submitting for grading a solution to a classwork or homework problem involves:

downloading the notebook to your computer, and
uploading the notebook from your computer to the Canvas submission page.

The first of these steps is performed by the "Download Notebook" button on the notebook as shown in the following figure.

A copy of the notebook file will be created on your computer. It will be saved on your computer wherever your settings indicated that downloaded files should be saved. Be sure that you know where downloaded files are saved on your computer because you will need to locate this file for the second step.

The second step, uploading the notebook for grading is shown in the next figure. You need to be on the Canvas Assignment page for the correct class day and the correct kind of assignment (i.e., Classwork or Homework). Be sure that you have selected the correct assignment in the menu at the top of the submission page. In the figure, the 3rd Classwork problem for Day 14 has been selected. As you can image, if you select the wrong day or kind of assignment you will get the wrong feedback and the wrong grade.

After selecting the correct assignment, click the "Upload" button. A window will appear on your computer so that you can locate the file you want to submit for grading (i.e., the notebook that you downloaded to your computer from the Jupyter server).

Once you have uploaded the file you will see any response in the Feedback area of the submission page. A correct answer will receive the feedback "Success." If the submitted notebook is not completely correct some feedback will be given indicating a mistake.

Lets Get Started!

You are now ready to start working with Jupyter Notebooks!