Template [Python]

1. Data types, data structures and indexing

1.1 Basics

Object, assignment, functions, how to comment and get help

# We can use Python as a calculator!

# Built-in functions can help execute things; we usually have to provide arguments

# Don't know how a function works? Ask for help!

1.2 Data types

Numeric: integer and float

String

Boolean

Not sure?

1.3 Collections

Lists

Lists are ordered collections of changeable elements

Can we add element to a list?

List inception: list of lists

Dictionary

Dictionaries are unordered collections of changeable and indexed elements

# Dictionairies are made of keys...

# ... and values

DataFrame

DataFrames are data structures containing labeled axes

# DataFrame are not a built-in type of Python; we must import an Python library to use them

Data frames

data.frame(vector1, vector2)	# bind vectors with the same length

# Df can be build from a list of lists

# Df can be build from dictionary

1.4 Dimensions

1.5 Indexing

Accessing elements of a list

Looking up values for a specific key

Getting an entire column of a DF

Int and Label indexing of DF

# integer indexing [row, col]

# label indexing [row, col]

1.6 Slicing

### PRO TIP

# Select rows with capital letters only

2. Files

Absolute paths

C:/Users/RonBumblefootThal/Documents/pythonFolder/MyFirstProject/Draft/IDon'tKnowWhatI'mDoing/etc.py

Relative Paths

~/I_love_my_project/CoolCode.py

2.1 Working directories

2.2 Save/write files

DF example

soa_tour = pd.DataFrame()

soa_tour['country'] = ['USA', 'UK', 'FRA', 'GER', 'BRA']

soa_tour['frequency'] = [39, 6, 6, 5, 3]

soa_tour['continents'] = ['north_america', 'europe', 'europe', 'europe', 'south_america']

soa_tour

# df_name.to_csv(PATH, header=BOOL)

2.3 Load/read files

From your PC

From URL

Metabolic rates data: http://sciencecomputing.io/data/metabolicrates.csv

url = "http://sciencecomputing.io/data/metabolicrates.csv"

Play around a little bit with this big DF... what can you do?

3. Control Flow

You already apply control flow when you decide how to go to work during winter.

For example:

• You take the metro if it's snowy

• You take the metro if it's cold

• You walk every other time

Let's code it now ;)

3.1 Conditional evaluation

Simple if statement

Structure:

if condition :

	do something

Example:

If/else statement

Structure:

if condition1 :

	do something

elif condition2 :

	do another thing

else :

	do something else

Example:

Nested statement

if condition1 :

	do something

else :

	if conditionA :

  	do another thing

  else :

  	do something else

Example:

Multiple conditions: AND & OR

3.2 For loops

Using a for loop you could plan your outings for a few days based on the forecast

What we are now familiar with:

What if we want to take into account the forecast for the next five days?

Can we still use our for loop?

Iterations

Structure:

for i in [] :

	do something for each i

Examples

# remember the len function? and how to access elements of a list?

If statement inside for loop

Structure:

for i in [] :

	if condition on i :

  	do something

  else :

  	do something else

Example:

# don't forget to correctly INDENT

3.3 Extras

Some logical operators

print (2 < 3)

print (2 > 3)

print (2 <= 2, 1 <= 2)

print (4 >= 4, 4 >= 3)

print (1 == 1)

print (1 != 1, 1 != 2)

print (not True, not False)

print (True or False, True | False)

print (True and False, True and True, False & True, False & False)

4. Functions

4.1 Syntax and arguments

Basic syntax

def function_name(args) :

	result = do something with args

  return result

# name and arguments

# what the function does

# what the function returns

# apply function on values

# apply function on variables

Using built-in functions

4.2 Scope

Variables can exist in a global or a local scope.

Remember, the abs_temp_difference function is returning the value of the abs_result variable

# what will 'abs_result' return?

Here is a second example:

# global variables

# global and local variables returned: what is what?

# which variable does not exist in the global scope?

# what is the value of 'squirrels'?

4.3 Integration

Combining functions and control flow

Let's go back to our forecast example.

Here's the forecast for an entire week:

# week forecast

weather_week = ['snowing', 'cloudy', 'snowing', 'clear', 'rainy']

temp_week = [-15, 3, -2, -23, 11]

# weekend forecast

weather_weekend = ['snowing', 'rainy']

temp_weekend = [-3, 2]

Let's build a function that will analyze either the week or the weekend forecast

def choose_transporation(weather, temperature) :

	for each day :

  	if snowing or cold :

    	'Take the metro'

    else :

    	'Walk'

# week transportation

# weekend transportation

4.4 Exercise: Animal Metabolism

This exercise will help you integrate the following:

• Files handling

• Control flow

• Function

Write a function to read a file if it exists and downloading it if it does not exist

# Pseudocode

function get_data(fn, url)

	if fn exist

  	open it

  else 

  	download from url

# remember the os librairy...

path = 'data/clean/'

fn1 = 'soa_tour_python.csv'

fn2 = 'this_file_does_not_exist.csv'

print (os.path.isfile(path+fn1))

print (os.path.isfile(path+fn2))

filename = 'metabolic_rates.csv'

url = "http://sciencecomputing.io/data/metabolicrates.csv"

Extras

Default values

# Define function