python_tuto.qmd

---
title: "Python tutorial"
format: 
  revealjs:
  #logo: img/cesab-logo.png
    theme: moon
    smaller: true
jupyter: python3    
---

## Setup

Setting up a local python environment is a pain...


![Source: http://xkcd.com/1987](img/py_nightmare.png){fig-align="centre" height="50%"}


## Setup

Easiest way : install Anaconda Navigator...

Editors: 
- IDLE = default
- Anaconda > Spyder, PyCharm, ... and RStudio too! File > New file > Python script


![Python prompt: >>> ](img/py_in_RStudio.png){ height="50%"}

## Setup

Online options:

- **Jupyter notebooks:** open from Anaconda

- **google colab :** (+) has google installed libraries and GPU/TPU power (limited GO). (-) to make one you need a google account



## Basics

Same programming rules: 

- named variables: 

`>>> a=50`
- use `+=` to increment/concatenate

`>>> a += a + 1`

- a list = multiple values in a variable. Each value is identified by its **key** (name). 

`>>> mylist = ['tic', 'tac', 'toc']`

- in Python, index starts at 0, not 1 (so NOT like in R): in mylist, the key for value toto is 0.  

`>>> print(mylist[2])`


## Basics

A common object to manipulate in Python are **dictionaries**: they're a pair of KEY:Value just like in lists, but here  keys in dictionaries aren't ordered. Use `{}` to initiate them (but still use `[]` to manipulate them).

`>>> mydico = {}` or 

`>>> mydico = dict(Lastname = "Petit", Firstname = "Cathleen", Pronounciation = "Kétline")`


Same conditional rules as in R: if, else, elsif --> NO !! it's **elif** (but who uses those..?!)

Otherwise same logical operators : `==, !=, >, >=, ... `

Another charming specificity is that **indentation matters** and will throw errors if ignored.




## A few commun built-in functions:

random(list) → choose random element of a list

len(list) → number of elements in list

max / min(list) 

str.split(separator) → transform str into list according to separator

list.append(value) → add a value to list (like c() in R)

list[key] = calls value associated to key

del list[key]

list.remove(value)

list.count(value) → counts number of occurrences of that value in the list

list[-1] → shows the last value of the list

list [a:b] → show values from a to b

x.extend(y) → concatenate lists x and y

lists of lists....


## Your turn !!

Write a script to ask the user their age, and give different answers depending on whether you think it's old or young.


## Answer:

```python

limit = 99

age = "How old are you ?"

if int(age) > limit:
  print("Wow, you're a living fossil !")
else
  print("Oh yeah, you're alright.")

```