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index.qmd
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index.qmd
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---
title: "A soft intro to Python (part I)"
format:
revealjs:
theme: dark
smaller: true
jupyter: python3
---
## Setup
Setting up a local python environment is a pain...
{fig-align="center" width="50%"}
## Setup
Easiest way : install Anaconda Navigator...
Editors:
- IDLE = default
- Anaconda \> Spyder, PyCharm, ...
and RStudio too! File \> New file \> Python script
{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 += 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 'tic' is 0.
`>>> print(mylist[2])`
## Basics
::: {style="font-size: 75%;"}
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`, `elseif`... (--\> NO !! it's **elif** instead of `elseif`... but who uses those anyways ?)
**Arithmetic operators :** the usual, but also: `%`, which means 'modulo' = is a multiple of. Returns 1 or 0 (True/False).
**Logical operators :** `==`, `!=`, `>`, `>=` ...
:::
## For loops
Syntax:
::: {style="font-size: 100%;"}
```{python}
#| echo: true
#| eval: false
string = 'Hello sunshine !'
for a in string :
print(a)
```
Try it !
:::
## A few commun built-in functions:
::: {style="font-size: 55%;"}
`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)
`del list[key]`, **NOT the same as** `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
`str.find(string)` → counts occurrences of str in string
`str.replace(where, what)`
`input(string)` → prints string and asks user for feedback (VERY INTERESTING)
`range(int)` → useful in for loops: for i in range(1, 10):
:::
## Libraries
Just like in R: built-in functions, but also packages of functions, called libraries.
Use `import library` to load them. Colab has many pre-installed libraries, but sometimes you need to activate them at the beginning of your session with `!pip install library` or `pip install library` or `pip3 install library` if you're using a local environment.
### Common libraries:
- math, random, numpy, ...
- scikit-learn, pytorch, SciPy, TensorFlow, Keras....: `import sklearn as skl` → data science.
- matplotlib : data viz. You can also choose to only import a function instead of the whole library: `import matplotlib.pyplot as plt`
- pandas : Python's tidyverse ;) Handles dataframes.
## Your turn !!
- play around with the different functions
### Exercise:
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 = input('How old are you ?')
if float(age) > limit:
print("Wow, you're a living fossil !")
else:
print("Oh yeah, you're alright.")
```
## Take home :
- indents !
- ":" after ifs and elses, rather than brackets like in R
- code execution by individual cells (on Colab/Jupyter) or entire script (Spyder, etc).
- python errors are usually quite precise: **read the error messages carefully**. Otherwise, absolute rule is: the internet has looooaaads of python forums, help pages, tutorials, bug fixes. A very active community.
## Homework :)
Generate a list of integers, and then show:
- the list
- the list in column format, displaying matching keys and values
- the sum of all elements of the list
- create a new list made of 5 multiples of the original list
- give min and max values of the list
- count occurrences of pair and odd numbers and sum them
## Quick games
Write a program to...
- throw a dice
- throw 2 dice
- Rock paper cisors
- guess a number between 1 and 1000 by indicating when the value is higher or lower
- hangman (without the graphical aspect)