Intro To Python

SWBATs

Print to the terminal using the print() function.
Use the correct naming convention to create and use variables.
Identify the common data types in Python str, int, float, bool, list, tuple, set, dict, None.
Create and invoke functions in python.
Use the ipdb library to debug Python code.
Use comparison operators in Python
Use Logical operators in Python
Use for and while loops in Python
Use List Comprehensions in Python

Installing Python

Mac

Install pyenv

Before installing Python, we first need to install pyenv, a version manager for Python. We will likely only use Python version for our last two workshops, but installing pyenv will make it simple to install newer versions later on.

Enter the following command in the Terminal:
```
brew install pyenv
```
Open your shell startup file (either .zshrc or .bash_profile) with the following command:
```
code ~/.zshrc
```
or
```
code ~/.bash_profile
```
Add the following to the end of the file:
```
if which pyenv > /dev/null; then 
  eval "$(pyenv init -)";
fi
```
We want to load pyenv every time we open a new terminal window; this will make sure that it does! Enter the following command to load your new settings:
```
source ~/.zshrc
```
or
```
source ~/.bash_profile
```
Install Python

Run the following command to install Python (you'll notice pyenv makes us put in the exact version instead of being able to just say 3.8 or 3):
```
pyenv install 3.8.13
```
After some time this should complete without any errors. It could take a while since you are compiling Python from source code.

Once this is finished we also need to tell pyenv this is our default version of Python using this command:
```
pyenv global 3.8.13
```
Ensure that these changes take effect by closing your terminal and opening a new one.

Check Your Work

You can verify that you have the correct version of Python installed by typing:
```
python3 --version
```
This command should show 3.8.13.

Install Pipenv

Another piece of software we will use in class is Pipenv. We will learn more about what Pipenv is later; for now, go ahead and install it:
```
pip install pipenv
```
After you have installed pipenv, modify your shell startup file (either ~/.zshrc or ~/.bash_profile) to add an export line inside the if statement we added earlier, after the eval line:
```
 if which pyenv > /dev/null; then
     eval "$(pyenv init - )";
     export PIPENV_VENV_IN_PROJECT=1
 fi
```
Save and close your shell startup file, then enter the following command once again to finish configuring your environment:
```
source ~/.zshrc
```
or
```
source ~/.bash_profile
```
Congratulations! If you've completed all these steps you are ready to code in Python!
Windows

Install pyenv

Before installing Python, we need to install the Python version manager pyenv. This is similar to the nvm tool we used to install Node.JS, except it controls which versions of Python we use on our system.

To install pyenv, we use the pyenv-installer.

Per the instructions on the pyenv-installer website, we start by running the following command:
```
curl https://pyenv.run | bash
```
Unlike nvm, pyenv does not automatically add its startup lines to your shell startup file.

The files that you have to change will depend on which shell you are running (you can check which shell you have by running echo $SHELL). Follow the instructions to update the startup files associated with the shell that you are running.

Open your .zshrc or .bashrc file with the following command:
```
code ~/.zshrc
```
or
```
code ~/.bashrc
```
Add the following lines:
```
export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
eval "$(pyenv init --path)"
```
To get your startup file to execute, restart your terminal.

Installing Dependencies on Windows and Ubuntu

For Windows and Ubuntu users you will need to install some extra dependencies for Python. (See here for more information about the prerequisites: pyenv Prerequisites)

First run this command to update your apt repositories:
```
sudo apt update
```
Next, run this command to install the packages listed on the pyenv:
```
sudo apt-get install -y build-essential libssl-dev zlib1g-dev libbz2-dev \
libreadline-dev libsqlite3-dev wget curl llvm libncurses5-dev libncursesw5-dev \
xz-utils tk-dev libffi-dev liblzma-dev python-openssl git
```
Installing Python

Run the following command to install Python (you'll notice pyenv makes us put in the exact version instead of being able to just say 3.8 or 3):
```
pyenv install 3.8.13
```
After some time this should complete without any errors. It could take a while since you are compiling Python from source code.

Once this is finished we also need to tell pyenv this is our default version of Python using this command:
```
pyenv global 3.8.13
```
Ensure that these changes take effect by closing your terminal and opening a new one.

Checking Your Work

You can verify that you have the correct version of Python installed by typing:
```
python --version 
python3 --version
```
Both of these commands should show 3.8.13

Installing Pipenv

Another piece of software we will use in class is Pipenv. We will learn more about what Pipenv is later; for now, go ahead and install it:

$ pip install pipenv

After you have installed pipenv, modify your shell startup file (either ~/.bash_profile or ~/.zshrc) to add an export line. This should go somewhere after the eval "$(pyenv init -)":

$ export PIPENV_VENV_IN_PROJECT=1

Congratulations! If you've completed all these steps you are ready to code in Python!

What is Python?

https://www.w3schools.com/python/python_intro.asp

The Print function

Similar to the console.log method in JavaScript, the Python print() function is used to print the specified message to the screen, or other standard output device.

The message can be a string, or any other object, the object will be converted into a string before written to the screen.

Common Data Types in Python

https://www.w3schools.com/python/python_datatypes.asp

String (constructor: str()) - The str type in Python is similar to the JS String data type. They are defined using single or double quotes only - no back tics in Python.
- For string interpolation, we use the f-string:
```
place_of_interest = "world"
greeting = f"Hello, {place_of_interest}"
```
Integers (constructor: int()) and Floats (constructor: float()) - Like Ruby, Python will consider any number written without decimals as an int (as in 138) and any number written with decimals as a float (as in 138.0)
Boolean - True and False (True and False need to be capitalized)
List (constructor: list()) - Comparable to the Ruby array, a list in Python is any set of comma separated data enclosed in brackets is a list.
Tuple (constructor: tuple()) - Tuples are just like list except they:
- Are immutable (cannot be changed once set)
- Created using parenthesis instead of square brackets
- There are only 2 tuple methods - Link
Dictionary (constructor: dict()) - A dict in Python is the JavaScript object equivalent that stores comma separated key/value pairs. One important difference is that the keys in dictionaries need to be strings. Other than that, everything else is the same.
None - Python’s version of Ruby’s nil or JS’s null or undefined

Functions in Python

Functions in Python are defined using the def keyword.
The name of the function, by convention, is like Ruby - snake_case
Parameters are still defined in parentheses
In JS, we used curly braces to define the function body. In Python, we will start the function body with a colon : and indent every line in the function body with 4 spaces.
Use the return keyword to return a value from Python functions.
If you are woking in the Python REPL in your terminal, end a function definition with another space.

Creating a virtual env

There are two types of environments that you can set up:
- Local Python env
- Virtual Python env
Your local Python env is going to be the Python related Software and Libraries that you have installed on your machine
The virtual env is an environment that you can create for a particular project and for this, we will use pipenv
To create a virtual environment using pipenv we can use the following command.
```
pipenv --python 3.8.13
```
The --python flag allows us to choose which Python version that we would like to use for this project.
This command will also generate one file for us:
- Pipfile - describes the dependencies that we have installed and the Python version.
We can now install packages like the debugger, ipdb
- pipenv install ipdb
You will notice that we have generated another file - the Pipfile.lock file:
- Pipfile.lock - describes all the dependencies our dependencies rely on. Like the npm package-lock.json file, the Pipfile.lock gives us the ability to reproduce a project env.

Control flow in Python

>: greater than
>=: greater than or equal to
<: less than
<=: less than or equal to
==: equal to
!=: not equal to

Logical Operators

Python has the same logical operators you'll find in many other languages, including JavaScript:

and: and. Returns True if both statements are true.
or: or. Returns True if one of the two statements is true.
not: not. Coerces the data to its boolean equivalent, then reverses it (True becomes False, and vice versa).

List Comprehensions

A list comprehension allows us to instantiate a list object and perform a for loop to populate its values in a single line.

Resources

List Comprehensions - W3Schools Link
Python through a Ruby lens - Link
Try/except - Link
Sequence Types
More on Lists
Range Docs
String Methods
Generator expressions

codetombomb/amazon-pgw-intro-to-python

Intro To Python

SWBATs

Installing Python

Install pyenv

Install Python

Check Your Work

Install Pipenv

Install pyenv

Installing Dependencies on Windows and Ubuntu

Installing Python

Checking Your Work

Installing Pipenv

What is Python?

The Print function

Common Data Types in Python

Functions in Python

Creating a virtual env

Control flow in Python

Logical Operators

List Comprehensions

Resources