Python

Overview

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Variables and Data

You can assign different types of informations to variables. Variable names cannot contain whitespace and cannot start with a number. These types of informations are datay types. A few basic ones in Python are integer numbers, floating point numbers, boolean types and strings.

my_age = 28                      # int
price_for_one_item = 0.5         # float
my_name_is_philipp = True        # bool
my_name_is_peter = False         # bool
my_name = "Philipp von Neumann"  # str
my_last_name = 'Neumann'         # str
 
print(my_name)
print(my_age)

Artihmetic

In Python you can just use the standard arithmetic operators and ignore whether the numbers are floats and integers. A division returns always a floating point number.

price_per_item = 0.5
amount = 10
 
order_price = price_per_item * amount  # mult
print(order_price)
 
shipping_cost = 3.0
 
total_cost = order_price + shipping_cost  # add
print(total_cost)
 
voucher = 2.0
total_cost = total_cost - voucher  # sub
print(total_cost)
 
brothers_cost = total_cost / 2  # div
print(brothers_cost)
 
# with // you will always get the result of a integer division
var2 = 13
var3 = 3
 
var4 = var2 // var3
print(var4)

You can also use this kind of shorthand notation for your operations:

var = 10
 
var += 2
print(var)
var = var + 2
print(var)
 
var -= 2
print(var)
var = var - 2
print(var)
 
var *= 2
print(var)
var = var * 2
print(var)
 
var /= 2
print(var)
var = var / 2
print(var)

Control Structures and Logic

Boolean and If-Statements

With comparison operators you can check if a statement evaluates to true or false. This is usefull when you want to execute parts of your program depending on this evaluation.

# == (Equal)
# < (Less than)
# > (Greater than)
# != (Not equal)
# <= (Less or equal than)
# >= (Greater or equal than)
 
my_bank_account = 130.0
 
i_am_broke = my_bank_account <= 0.0
 
# if-else statement
if i_am_broke:
    print("I am broke!")
else:
    print("I am not broke!")
 
gpu_price = 800.0
my_bank_account = my_bank_account - gpu_price
 
i_am_broke = my_bank_account <= 0.0
 
# if-else statement
if i_am_broke:
    print("I am broke!")
else:
    print("I am not broke!")
 
# if-elseif statement
my_age = 28
 
if my_age < 18:
    print("You are a child!")
elif my_age < 67:
    print("You are an adult!")
else:
    print("You are a pensioneer!")

(Virtual) Environments

Python projects exist in virtual environments, short for “venv”. A venv helps to define a list of libraries which are necessary for a specific project. Normally with Python you don’t install libraries globally, because projects can rely on specific versions of a library. A good practice is to exclude your venv dir from version controlling.

Creating a venv

• You can create a venve withthe terminal command python3 -m venv .my-venv
• after this you can activated it with source .my-venv/bin/activate
• and deactivate with deactivate

Requirements

A requirements.txt is file with a list of Python libraries, that are necessary for a specific Python project.

• you can ‘freeze’ your dependencies of the project in a text file via pip3 freeze > requirements.txt
• after this someone can install the dependencies with pip3 install -r requirements.txt

Python in Emacs

Configurations

I use Python mostly in Emacs. For this you need to configure your Emacs properly. I use the LSP-Mode and some other packages. A few will follow.

Commands

• start your Python interpreter with C-c C-p
• run a line from a file in interpreter with C-c C-e
• run your file in interpreter with C-c C-c

Anaconda

Anaconda is a distribution of Python and R. It allows easy installation of a Python interpreter + various data science packages.

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