Python in CS 1110

Python comes in several shapes and sizes. To make sure that everything works properly, we require that every single person in the course use the same version of Python. You are free to either work in the labs or to use your laptop. But whatever the case, your version of Python must be the same as what we are using in the labs. Hence, even if you already have Python installed on your computer, we ask that you install a new version (see instructions below) so you can be consistent with everyone else.

As you will see, these instructions are a bit long. Installing Python is often much more complicated than simply using it. As many people in this class have not programmed before, we have tried to make installation as simple as possible via step-by-step instructions. You are not expected to understand what many of these steps are doing. Furthermore, these instructions are lengthy mainly because we are trying to support as many operating systems as possible. In practice, you should be able to finish the installation in 15-20 minutes.

If you have problems, and if you have a laptop, the best thing to do is to bring it in to someone to look at. Any of the course staff can help you with this. If you cannot bring in your computer, we have provided you with some instructions below. If you are having difficulty with these instructions, please post on Piazza or send email to Kevin Cook.

Table of Contents

• Installing Python
  • Installing on Windows
  • Installing on MacOS
  • Installing on Linux
• Getting Started with Python
  • Running Python Interactively
  • Testing a Module
  • Troubleshooting Catalina NEW
• Installing Atom
• Using GitHub

Installing Python

While installing the base Python package is usually straight-forward, getting add-ons for Python can be a bit tricky. That is why we have decided to standardize on the Anaconda version of Python. This is a free version of Python that is used by many courses on campus. It contains a lot of add-ons, limiting the number of things you need to install later.

Once you have the base Python install, you need to install the “Cornell Extensions”. These are 3rd party extensions packaged by us (and sometimes made by us) to fit into Python. These extra packages include things like graphics capabilities to make games and flashy applications.

Before you install these, be sure to completely read the instructions for your operating system. While you are unlikely to make any mistakes, it is best for you to do things in exactly the order we tell you to. As we said, you do not need to understand what is going on here.

Installing on Windows

We require that all students with Windows use Windows 10. This version has been out long enough that no one should be running Windows 8 or 7 anymore. If you are using an older version of Windows, we recommend that you upgrade now before the semester starts. If your machine cannot support Windows 10you will need to work on the lab computers.

For this class, we need to use Python version 3.7.6. This is not the most recent version of Python. However, our tests have shown that more recent versions of Python are not stable, and are not capable of completing the course assignments. If you have installed a more recent version of Python, you will need to install this version to “roll it back*. Even if you have Anaconda installed already, it is safest if you install from the button below to guarantee that you have the correct version.

Installing Anaconda for Python 3.7.6

Use one of the two links above to install the correct version for your operating system. Most modern Window installations are 64-bit. However, if you are unsure, download the 32-bit version. The 32-bit version is guaranteed to work on all systems.

The file that you download is an installer app. Simply double click on it and follow directions. At one point in the installer, it will ask you whether you want to install for yourself or for all users. Select the option “All Users (requires admin privileges)”, as shown below.

On the next page it will ask you what directory you want to install in. By default, it will install in C:\ProgramData\Anaconda3. We need this folder for Cornell Extensions, so leave this alone and click Next.

Finally, you will see a page with check boxes talking about your Path. You must select the top box, even though it warns you not to. If you do not check this box, you will not be able to use Python from the PowerShell.

When you are done installing, you will receive some information about an application called PyCharm. While you are not prohibited from installing this program, we will not be using it this semester, and we will not provide help on how to use it.

Installing the Cornell Extensions

Download the file from the link above. After downloading, you will see that this is a folder with a zipper on it. Double click on the folder. This will open an Explorer Window with another folder inside of it called CornellExtensionsInstall Drag the CornellExtensionsInstall folder on to your Desktop. This is important, as the installation is not guaranteed to work if you click on the installer while it is still inside the folder with the zipper (files inside of zipped folders are not “real” until you pull them out).

Now that you have a copy of CornellExtensionsInstall on your Desktop, open this folder (again, not the one in the zipped folder!). Inside, you should see the following two items:

Double-click on the file that is named install. This will pop up a window with a lot of scrolling text in it. Do not close the Window until you see the line that says “Installation Complete”, and asking you to hit a key. If you close the Window too early, you will have to install a second time.

On some Windows systems, the security settings may prevent you from installing Cornell Extensions. On those systems, you will see a security message like the one below.

If this happens to you, click on the “More info” link. When you do that, the information message should now look like this:

Click the “Run anyway” button to complete the installation.

Once you have finished with the Cornell Extensions, you should test your installation

Installing on Macintosh

While Macs are a great platform to run Python on, there is a major problem with Mac and Python caused in the past year. Apple broke something in Mojave (10.14), and did not fix it until they released Catalina (10.15). So you cannot run the latest Python with Mojave. The obvious solution is to upgrades to Catalina. Except that Apple stopped supporting 32-bit applications in Catalina. If you have a lot of applications older than 3 or 4 years old, this can be an issue (your instructor lost half his Steam library). So we can understand if you do not want to upgrade to Catalina.

The correct version of Python to install therefore depends on your operating system. If you do not know what you are running, go to the Apple menu and choose about this Mac. If you are running Catalina, you need to install Python version 3.7.6. This is not the most recent version of Python. However, our tests have shown that more recent versions of Python are not stable, and are not capable of completing the course assignments. If you have installed a more recent version of Python, you will need to install this version to “roll it back*. Even if you have Anaconda installed already, it is safest if you install from the button below to guarantee that you have the correct version.

If you are running Mojave, you need to install an even older version of python, Python version 3.6.5. We do not use any of the new features in Python 3.7, so you will be okay if you use this older version of Python. Versions of MacOS older than Mojave should also use version 3.6.5.

Installing Anaconda for MacOS

Use the above link to install the correct version for your operating system. The file that you download is an installer app. Simply double click on it and follow directions. You may wish to change the install location on this page:

However, there is something weird with the MacOS installer when you do this. In particular, you may see the following error:

This problem is easy to solve. If you just click on the house, it will now look like this.

It is okay for you to install Anaconda this way. However, we would prefer that you install it for all users instead. Select the hard drive icon below the house. When you are done, it should look like this.

Select the button Choose Folder to the right. This will tell it where to put Anaconda. We recommend that you put it in the Applications folder.

If you are using Catalina (10.15), you should be aware that MacOS has significantly increased security restrictions in this version of the OS. You must give permission to everything that the system thinks is unusual. This installer is one of those unusual things. The installer will appear to stall for a while, and then you will get this message:

Click OK and the installation should complete.

When you are done installing, you will receive some information about an application called PyCharm. While you are not prohibited from installing this program, we will not be using it this semester, and we will not provide help on how to use it.

Installing the Cornell Extensions

The last step is to install the Cornell Extensions for CS 1110. Download this file from the link above. After downloading the file, double click on it to unzip the contents into a folder somewhere on your computer.

Once again, you see will a package installer. Double click thid installer. You may see a warning telling you that this is not an official installer (because we made it). If that happens, you will need to control-click the installer and select Open from the drop-down menu.

If the installer launches properly, you will see the following window:

Follow the directions for the installer. Your installation is now complete.
Once this is done, you are now are ready to test your installation.

Installing on Linux

Linux installation is possible, but it is not as straight-forward as the two main OS options. In particular, to install on Linux, you have to be comfortable with the Terminal and be ready to install files with a package installer. If this sounds daunting to you, you might want to rethink about whether you want to use Linux just yet.

For this class, we need to use Python version 3.7.6. This is not the most recent version of Python. However, our tests have shown that more recent versions of Python are not stable, and are not capable of completing the course assignments. If you have installed a more recent version of Python, you will need to install this version to “roll it back*. Even if you have Anaconda installed already, it is safest if you install from the button below to guarantee that you have the correct version.

In the past, we have had install parties for Linux users. We have worked to make the instructions more self-sufficient this year. However, if there is still demand for a Linux install party, post your request on Piazza.

Installing Anaconda for Python 3.7.6

Use one of the two links above to install the correct version for your operating system. If you are in doubt, use the Intel version, as it is unlikely that you are working with a PowerPC machine.

This is not a graphical installer. To install it, you must navigate to the folder with the downloaded file and run it with bash. For example, if you downloaded the 64-bit version, you would type:

   bash Anaconda3-2020.02-Linux-x86_64.sh

You must use the “bash” command even if you are not using the bash shell.

You may install Anaconda where ever you wish. By default, it installs in your home directory. However, we prefer to install it in /usr/local. The choice is up to you.

Installing the Cornell Extensions

Because Linux platforms are so different, there is no one-click installer for Linux. In particular, we would need to know whether you are using apt-get (Debian, Ubuntu) or yum to install software. So we will let you do this on your own. There are two important steps.

Installing Kivy

Kivy is the graphics library that we will be using for several of the assignments in this class. In the past, students have had to compile this library from source code. However, Kivy now has installers for several flavors on Linux.
Look at the downloads page for more information.

For Ubuntu, you will notice that the instructions suggest using apt-get. This only works for installing Kivy into the the official Ubuntu Python 3. This version of Python is old and missing a lot of packages. Therefore, we suggest that you install using PIP. The exact sequence for installing on Linux (assuming you are running Python 3.7.6) is as follows:

    > sudo pip install --upgrade pip setuptools
    > pip install kivy

If this does not work, and you are using Anaconda, you may want to use the conda command instead. Kivy is an optional Anaconda package using Conda Forge. Simply use the command

    > conda install -c conda-forge kivy 

Installing introcs

If you got Kivy working, then you are almost done. The last step is the easiest. You need to install the introcs package using PIP. The command is

    > pip install introcs

Once this is installed, you are are ready to test your installation.

Using An Alternate Version of Python

If anything goes really wrong, you may just want to use the built-in Python 3 provided by your version of Linux. It is not ideal (most are still using 3.5 or are even using the problematic 3.8), but it will get you through the course. However, if you go your own way, there are several packages that you must install (using PIP). All of these packages are in addition to Kivy and introcs.

• tkinter
• pillow
• numpy
• scipy
• matplotlib
• requests
• dateutil

Keep in mind that this option may require you to build Kivy from source. If you cannot figure out how to do that, you may want to rethink using Linux for the semester.

Getting Started with Python

Now that you have installed Python, it is a good idea to test it out. While you do not need to know anything about Python yet, you do need to learn how to run Python programs that are already made for you.

Running the Python Shell

The first thing that you need to do is to familiarize yourself with command shell for your OS. The command shell is a text-based version of the Windows Explorer or Finder; you can use it to move and rename files and folders. It is also how we will run Python in this class.

Using the command shell requires a bit of practice, so we have created a separate page of instructions for this. Right now, all you need to know is how to start up the command shell. You do not need to know any special commands. Start the command shell for your OS and type

 python

This will put you in the “Python Interactive Shell”.

The Python Interactive Shell looks exactly like the command shell except that it takes Python commands (and does not respond to operating system commands to list files or change the working directory). While the command shells are different for all operating systems, the Python Interactive Shell should look and behave exactly the same way for everyone. On Windows, it will look something like this.

The >>> symbols are the prompt. To get the shell to do something, just type a Python command. For example, type

 >>> 1+1

and hit Return (do not type the >>>; it is already there). See what happens?

To exit the Python Interactive Shell, type quit() and hit Return. You can also exit by typing Control-D.

Testing a Script

It is possible to run Python script from the command shell as well. A script is a file (ending in suffix .py) containing Python code. We will use them throughout the course. To run a script, you type

 python <filename>

from the command shell. Do not try to type this in the Python Interactive Shell. This can be a bit confusing at first; it is important to keep the following straight:

• The command shell is a program for accessing files via text based commands. You start Python in this program, but it is not Python.
• The Python Interactive Shell is a program that runs inside the command shell. You can tell it is running by the presence of the >>> prompt.

Running a module does not start the Python Interactive Shell. It runs all of the commands in the file, and then quits immediately when done with the file.

To test that your installation is working properly, we have a cute Python module that displays a GUI with the phrase “Hello World!” inside it, as shown below.

To try out this module, download the file hello_tk.py and put it in some easy to find folder. Open up a command shell and navigate to this folder using the drag-and-drop trick for changing directories. Then type the command

 python hello_tk.py

If you get the window shown above, congratulations! You have successfully installed the proper version of Python necessary for this class.

If the Window does not show, look very carefully at the error messages. If it says it cannot find the file hello_tk.py, then you did not use the drag-and-drop trick correctly. We recommend that you practice with the command shell tutorial some more. Otherwise, there is a problem with your installation of Python. Post your error message to Piazza and we will try to help you out.

If you have the message working we recommend one more test. There are actually two different ways to create GUIs in Python. One is called TCL/Tk. The other is Kivy (which you installed as part of Cornell Extensions). The test above is for TCL/Tk. You should test out Kivy as well. To do that, download the file hello_kivy.py and repeat what you did with hello_tk.py. That, is navigate to the folder with the file and type

 python hello_kivy.py

The window that pops up should look pretty much the same as before, except that it will be of a different size and in a different location. If this script fails, but the TCL/Tk script worked, that means you did not properly install Cornell Extensions. Contact a staff member if you need help.

Troubleshooting Catalina

Catalina (MacOS 10.15) is a notoriously problematic upgrade that has caused problems for people all across the industry. That is because it changed so many things about how the Mac used to work. First of all, it eliminated 32 bit apps. But it also did something else that directly affects us in this class: it changed how the Terminal works.

The Terminal relies on a special program called a shell that tells it how to process the text based commands. For many years, MacOS – just like the vast majority of Unix – used the bash shell. In Catalina, they changed to zsh. It seems that, if you are a new Mac user – so you are using Catalina and have never used an older version of MacOS – the lack of any bash settings is confusing the Anaconda installer.

But we have a fix for you Catalina users. You need to do the following steps:

1. First make sure you are running zsh and not bash. To check, type

   echo $SHELL

2. While inside of the Terminal type

   touch ~/.zshrc

3. Find the correct path (with all of the slashes to Anaconda). We talk about paths in the videos of Lesson 0. The default Python 2.7 is at path

   /usr/bin/python

   Most (but not all of you) should have installed Anaconda at

   /Applications/anaconda3/bin

4. Open up .zshrc in TextEdit by typing (in the Terminal)

   open ~/.zshrc

5. Add the following line to this file

   export PATH="path-to-anaconda:$PATH"

   with those quotation marks, but putting in the correct path. So in most cases, this will be

   export PATH="/Applications/anaconda3/bin:$PATH"

6. Save and quit the file.
7. Quit and restart the Terminal.

This should fix your installation. If it does not, please see a consultant for help.

Installing Atom

The last program to install is Atom Editor. Unlike Python, you will not use this program right away. In fact, we will not start to use it until the third week of class. The purpose of Atom is to make these mysterious modules that you tested in the previous step.

Technically, you can write Python modules in any text editor (e.g. a Word processor that only produces text and does not have fonts or fancy formatting). NotePad and WordPad are text editors in Windows, while TextEdit is provided by MacOS. The reason we use Atom is that it is the same across all platforms. That allows you to collaborate with partners who might be working on other operating systems. Some people prefer Sublime Text, but that program is not free. The program VS Code is an acceptable alternative, but it is not properly configured for Python out of the box and requires significant customization.

To install Atom, click the button above to take you to the Atom website. You should see a yellow “Download” button, which has your computer system’s OS information above it. Click on that button.

If you are using a Windows computer, the downloaded file will be an .exe file. Double click it and Atom should install automatically. For Linux computers, install the .deb file and then double click on it. You should then be able to install it using your package manager.

If you are using a Mac computer, the downloaded file should be a .zip. Double click on that .zip file, and then drag the resulting Atom.app to your applications folder. The first time you attempt to open it, it may warn that it is an unverified application from the internet. Ignore this and click open on the window that pops up.

Configuring Preferences

One of the most controversial aspects of Python is that it treats spaces and tabs very differently. If you accidentally put a tab in your program, it will cause your program will crash. And you will have a hard time finding it because both tabs and spaces look exactly the same.

Most of the time, this is not a problem. However, we must first configure Atom so that indentation is consistent across all of our files. First, open Atom. Then, open the Settings menu option; in Windows, it is under the File category, and in Mac, it is under Atom (and is named Preferences). Then, in the settings window that opens, select the Editor category, and scroll down. First, check the boxes “Show Indent Guide” and “Show Invisibles” so that your settings match this image:

Click for Bigger Image

This will allow you to see both tabs and spaces, and to tell the difference between both. Spaces will look like light dots which are centered vertically on each line. Tabs will look like two ‘>’ characters next to each other. These are illustrated in the examples below.

Atom with Tabs (Bad)		Spaces Only (Good)

Continue scrolling down. Change the value in “Tab Length” to 4, and click on the value in “Tab Type”. This should open a drop-down menu. Select “soft”. This will make Atom automatically replace all Tabs you input with 4 spaces. After configuring, these two settings should look like this:

Click for Bigger Image

Using GitHub

We do not require the use of GitHub for this course, as it is a bit too advanced for many students. However, we know that some of you will use it anyway, particularly for sharing assignment code with your partner. Because of our academic integrity policy, we need to put strict rules on its use.

The free accounts that you get from github.com are publicly viewable. That means anyone can see them, and anyone can download code from them. This means that if you put your code on GitHub, and another student downloads it, you will be held liable for cheating, even though you may have no idea who this other person is. In fact, any code we find in publicly visibile in GitHub will constitute and academic integrity violation whether or not anyone copies it.

If you want to use a code repository, you should use the official Cornell GitHub instead. Any projects that you put here will be protected and cannot be accessed by other students. You will not be held liable for security leaks that are not your fault.

We know that this is inconvenient for students that would like to show code to prospective employers. However, there has been enough abuse of this in recent years that we have had to take a stricter approach to GitHub. We recommend that you share your code through a private repository or else work on another Python project in your own time.