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klarna-python

Getting started guide

Long ago (before Jan. 1, 2020), there were two major versions of Python: 2 and 3. But now, although it is possible to develop in Python 2, it isn't recommended (and in this class will actively be discouraged). Python 2 is also being deprecated which means that the libraries you'll use will stop having active updates and support.

Python is a cross-platform programming language, which means it runs on all major operating systems. Here, we'll make sure Python 3 is setup correctly on your computer, and have you run your first python script.

Installing Python

Each OS comes with it's own flavour of Python and there are small details different to each OS. To make sure that we all have a standard working environment, we will first install anaconda. Anaconda is a bundled python environment which comes with a lot of DS & ML libraries and allows for easy installation of packages for your user only without needing admin privileges.

Windows

Installation

  1. Download Anaconda for Windows, v3.7 and start installation.
  2. Select “Just Me” during installation.
  3. Select C:\anaconda3 as your install directory.
  4. In the final screen before installation, check "Register anaconda3 as my default Python3.7 installation".

Verifying installation

  1. In your start menu, search for Anaconda Prompt and open it. Type python and press enter to get your Python prompt.
  2. You should see a >>> symbol. This symbol is called the prompt and it indicates that the computer is ready to accept our input. It is here that we'll type our python code. If you see a C:\User.. something (that is, a regular windows prompt), type python to get to the python prompt.
  3. Type print("Hello World!") and you should see the output!

Troubleshooting

  • For the complete install instructions, click here.
  • If you're still having problems, please check with your instructor.

MacOS

Python is already installed on most Macs. However, it's a non-standard setup so we'll re-install python using anaconda.

Installation

  1. Download Anaconda for MacOS, v3.7 and start installation by double-clicking the downloaded file.
  2. On the destination select screen, choose Install for me only.
  3. On the Installation Type screen, click on Change Install Location.
  4. Set the install location to ~/anaconda3.
  5. During the installation, you will be asked “Do you wish the installer to initialize Anaconda3 by running conda init?". Answer yes to this question.

Verifying installation

  1. Open spotlight: Press ⌘ + Space
  2. Search for iTerm (alternatively Terminal if you don't have iTerm installed).
  3. You should see a ➜ or >>> symbol. This symbol is called the prompt and it indicates that the computer is ready to accept our input. Type python on the prompt to launch the Python shell.
  4. You should see a >>> symbol. This again indicated that the Python shell is ready to accept our inputs and it's here that we'll type our python code.
  5. Type print("Hello World!") and you should see the output!

Troubleshooting

  • For the complete install instructions, click here.
  • If you're still having problems, please check with your instructor.

Ubuntu/Debian

Installation

  1. Open Terminal (Ctrl + Alt + T).
  2. Go to your downloads folder: cd ~/Downloads.
  3. Download anaconda: wget https://repo.anaconda.com/archive/Anaconda3-2020.02-Linux-x86_64.sh.
  4. Run the file: bash Anaconda3-2020.02-Linux-x86_64.sh.
  5. When the installer asks for installation location, type ~/anaconda3 if it's not the default.

Verifying installation

  1. Close and reopen the terminal.
  2. Type python on the prompt.
  3. You should see a >>> symbol. This symbol is called the prompt and it indicates that the computer is ready to accept our input. Type python on the prompt to launch the Python shell.
  4. Type print("Hello World!") and you should see the output!

Troubleshooting

  • For the complete install instructions, click here.
  • If you're still having problems, please check with your instructor.

Terminal and shell

If you're feeling confused about what's the difference between a terminal, a shell and a prompt, don't worry and continue reading this section!

The shell is a computer program which processes user commands, executes those commands and then returns the output to the user. When the shell is launched it puts up a prompt which is simply a special symbol that indicates (or prompts) the user that the shell program is waiting for the user's input commands. The most common prompt symbols are >>> and ➜. A terminal refers to a wrapper program which runs a shell which allows the user to interact with the computer. Decades ago, the terminal was a physical hardware thing but nowadays the terminal was abstracted into software. Let's see these concepts in practice.

  • Open spotlight: Press ⌘ + Space

spotlight.png

  • Search for iTerm (alternatively Terminal if you don't have iTerm installed).

spotlight_terminal.png

  • This will launch the terminal which by default runs a Unix shell (MacOS is a Unix based operating system) which allows the user to interact with the operating system by executing different commands. Common Unix shells on most Macs are bash and zsh. In the example below, we see that the terminal is running the zsh Unix shell.

terminal_landing_screen.png

There are many useful zsh commands that allow the user to interact with the operating system, as well as start up different programs. For example, we can print the current working directory (pwd), list the contents of the current working directory (ls), change the current working directory (cd), etc.

  • In our example, the terminal launched in the home directory (~ is a special filepath symbol that indicates the user's home directory). Let's get the full filepath by running the pwd command.

terminal_pwd.png

  • Let's next see the contents of our home directory by executing the ls command.

terminal_ls.png

  • Let's create a new empty directory called my_awesome_directory. We do this by running the mkdir my_awesome_directory command. After that let's list the contents of the current working directory (which is still the home directory) to see that we've indeed created our new directory.

terminal_mkdir.png

  • Let's change the current working directory from the home directory to our newly created directory. We do this by running the cd my_awesome_directory command. We now see the current working directory change (next to the prompt) and we can retrieve the new full filepath by running the command pwd.

terminal_cd.png

In short, we can use the terminal to run a Unix shell (zsh in the examples above) to interact with the operating system. There are many useful commands that allow you to do any operation you can do with a regular graphical user interface (and more) such as creating, copying and moving files. The Unix shell can be a very powerful tool once you learn to master it over time that will allow you to perform and automate many complex task in the form of scripts.

The terminal can also be used to run a Python shell which allows the user to execute Python commands.

  • Execute the python command in the terminal.

terminal_python.png

  • This will launch the Python shell prompting the user to give Python commands.

python_shell.png

  • We can now execute Python commands such as an addition (1+1) or a print statement (print("Hello world!")).

python_shell_commands.png

  • Notice that the Python shell does not recognize any of the zsh commands we learned in the previous section!

python_shell_invalid_commands.png

  • We can exit the Python shell by typing exit(). This will resume the zsh shell that was running prior to launching the Python shell.

python_shell_exit.png

Although the Python shell is a handy tool to quickly check e.g. the syntax validity of a Python command or the output of a Python function, it is not very useful for writing full programs as it requires the user to manually enter each command one-by-one. Instead, Python programs are written as text files (called Python scripts) which are then fully executed with Python.

Installing a text editor

Programming is about writing text about just as much as computer science is about computers - that is to say: not very much. However, putting text down efficiently, being able to manipulate the text without having to think about is crucial to not having your chain of thought disrupted. Aside from that, a good text editor helps you in several ways:

  • Jumping to definition of a function defined in a different file
  • Code debugging write within the editor
  • Code refactoring
  • Manipulating text a lot more efficiently vs just normal Copy and Paste
  • Linting: Showing when you're writing incorrect code/writing code in a bad style
  • Etc.

You don't need to worry about this all this just now. However, we want to start you off with a text editor that easy to get started with but is very powerful and can grow with you: Visual Studio Code

Windows

  1. Download the Visual Studio Code installer for Windows.
  2. Once it is downloaded, run the installer (VSCodeUserSetup-{version}.exe).
  3. On the Select Additional Tasks screen, make sure to check:
    • Create desktop icon
    • Add "Open with code" to windows file explorer file context menu
    • Add "Open with code" to windows file explorer directory context menu
    • Register code as an editor for supported file types
    • Add to PATH
  4. By default, VS Code is installed under C:\users\{username}\AppData\Local\Programs\Microsoft VS Code. This setup doesn't need admin privileges.

Open and check VSCode to see whether the installation was successful:

  • Go to desktop and double click VSCode icon
  • VSCode should open

Note: If you are having trouble starting VSCode, your .NET Framework might be old. You need to update it.

  • Check which version you have by running reg query "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\full" /v version in the command line (Start menu > search for cmd > open > paste the command)
  • If your .NET version is old, download and install the latest version from

MacOS

  1. Download Visual Studio Code for macOS
  2. Open the browser's download list and locate the downloaded archive
  3. Select the 'magnifying glass' icon to open the archive in Finder
  4. Drag Visual Studio Code.app to the Applications folder, making it available in the macOS Launchpad
  5. Add VS Code to your Dock by right-clicking on the icon to bring up the context menu and choosing Options, Keep in Dock

Open and check VSCode to see whether the installation was successful:

  • Open spotlight (⌘ + Space)
  • Start search for VSCode by typing visual studio code. You should see Visual Studio Code in the dropdown list
  • Press Enter to open VSCode

To make VSCode launchable from the command line:

  • Open VSCode from dock or from spotlight (⌘ + Space)
  • Open the Command Palette (⇧⌘P) and type 'shell command' to find the Shell Command: Install 'code' command in PATH command.
  • Restart the terminal for the new $PATH value to take effect. You'll be able to type 'code .' in any folder to start editing files in that folder

Linux

  • If you have snap installed, then run
sudo snap install --classic code
  • If you don't have snap, download the deb archive, navigate to the download directory in terminal (cd ~/Downloads) and run
sudo apt install ./<file>.deb

Open and check VSCode to see whether the installation was successful:

  • On a terminal, type code to launch VSCode
  • Or, you can also find VSCode in the launcher

Install Python VSCode extension (Windows/Mac/Linux)

  • Click on the Extensions Icon on the left sidebar. It looks like this:

extensions-view-icon.png

  • In the search bar, search for Python
  • Click Install
  • Choose Select Python Interpreter and select the anaconda python you just installed at the Path ~\anaconda3\python.exe, name should be something like Python 3.8.8 64-bit ('base': conda).

Running the Hello World Program from within VSCode

  • Make a folder called python_work somewhere on your system for your projects. (It’s best to use lowercase letters and underscores for spaces in file and folder names, because these are Python naming conventions)
  • Open VSCode
  • Make a new file (⌘/Ctrl + N or File > New File) and save it as hello_world.py in your python_work folder
    • The .py file extension is used for all python files
    • It allows you to directly open the file in VSCode
    • It also allows VSCode to detect that this is a python program and enable all python specific features in the editor
  • After you’ve saved your file, enter the following line:
print("Hello World!")
  • To check whether the python interpreter (that we installed earlier) has already been recognized by VSCode, look at the lower left corner of the screen and find the status bar. You should see something like this:

VSCode screenshot

  • See the Python 3.8.8 64-bit line? That means VSCode knows where Python is installed
  • If you don't see this information, you'll need to tell VSCode where to find Python. For this:
    • Open the command palette in VSCode:
      • Mac ⇧⌘P
      • Windows/Linux: Ctrl + Shift + P
    • Start typing: Python: Select Interpreter to search for the command
    • Select one of the options shown to you which has conda in the name ​

If nothing python-related shows up when you start typing, make sure you installed that python VSCode extension.

Running Hello World Program

You should now be able to run your program successfully. Run hello_world.py by selecting Run > Run without debugging (you'll also be able to see the shortcut you can use to do this the next time - it's Ctrl + F5 on all systems)

In the terminal, you'll see something like the following output​

$ cd /Users/prasoon.shukla/tmp/python_work ; env python /Users/prasoon.shukla/.vscode/extensions/ms-python.python-2020.6.89148/pythonFiles/lib/python/debugpy/launcher 52156 -- /Users/prasoon.shukla/tmp/python_work/hello_world.py

Hello world!

The first line is just VSCode setting up the python environment correctly and executing the file from the CLI. The second line is the output of the program! ​ If you don't see this, or if you have problems anywhere else during this setup, don't hesitate to contact Prasoon. ​

Running Python Programs from a Terminal

Most of the programs you write in your text editor you'll run directly from the editor, but sometimes it's useful to run programs from a terminal instead. For example, you might want to run an existing program, without opening it for editing. ​

You can do this on any system with Python installed if you know how to access the directory where you stored the program file. To try this, make sure you've saved the hello_world.py file in the python_work folder on your desktop.

​ Most of your programs will run fine directly from your editor, but as your work becomes more complex, you might write programs that you'll need to run from a terminal. ​

On OS X/Linux

The terminal command cd (change directory), is used to navigate through your file system in a terminal session. The command ls (list), shows you all the nonhidden files that exist in the current directory. Open a new terminal window:

  • For Mac: spotlight > iTerm, or if you already have the terminal open, ⌘T
  • For Linux: Ctrl + Shift + T or search terminal in launcher

Then, issue the following commands to run hello_world.py:

cd Desktop/python_work/ 
ls
python hello_world.py

The first command navigates to your work folder which is in the Desktop folder. The next command lists the files and directories within that folder. Finally, we run the python script using the commend python hello_world.py It's that simple. You just use the python3 command to run python programs. ​

On Windows

The terminal command cd (change directory), is used to navigate through your file system in a terminal session. The command dir (directory listing), shows you all the nonhidden files that exist in the current directory. Open a new terminal window (start Anaconda Prompt from start menu) and issue the following commands to run hello_world.py:

cd Desktop\python_work
dir
python hello_world.py

The first command navigates to your work folder which is in the Desktop folder. The next command lists the files and directories within that folder. Finally, we run the python script using the commend python hello_world.py

​

Other useful connection options

While running a script, either from a terminal or from a text editor is a great way to develop, sometimes you want the flexibility of being able to run small snippets of code and seeing the output with lower overhead. ​ We're going to give you two options: jupyter notebooks and the ipython extension. ​

Jupyter Notebook

Jupyter notebooks are an open-source, interactive web application that allows you to write and run code in a number of languages. It has become almost the defacto means of developing code in Python, especially in Data Science. ​ Jupyter comes pre-installed when you install anaconda so we don't need to install it manually.​

Open a terminal (or use the one you still have open from above) and enter the following command:

jupyter notebook

This should open a jupyter notebook within your web browser. ​ If there are problems, contact your instructor. ​

IPython

IPython provides a python session that is interactive. It's worth having for the text completion. IPython also comes preinstal​led with anaconda.

Now when you want to test python quickly run the following in your terminal:

ipython

which will spin up an interactive python session. ​

Final thoughts on setup

If this was hard, or you struggled, please don't worry. Some of this setup is tricky. We wanted to take the time this week to make sure everyone is set up correctly, so when we start working on projects next week we're all on the same page/system. ​ Feel free to reach out to any of the instructors, and we'll find the time to sit down and get you set up correctly.

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