Python Cheat Sheets (Python, Django, Pipenv)

In this article I'll be posting a series of code snippets, gotchas and syntax description for Python and some of its notable projects like Django, Flask, Pandas, Numpy, etc.

The idea is to have a single stop resource for those obscure and sometimes forgettable snippets that you need in your Python projects.

Depending on your level of experience, some of this snips will be too basic or to complex for you.

Python

A more complete PDF version can be found in the Python Crash Course Site.

Python Variables

Syntax	Comments
`True` `False`	Contrary to other languages, they are capitalized
`"string" 'string'`	Both quotes are valid
`a,b = b,a`	Variable swap

Adding comments in python

Syntax	Notes
`# ...`	Pound sign comment a line
`"""`	Triple quotes allow you to comment a function or class when placed After the function declaration

Input from the console

Syntax	Notes
`input()`	Receives input from the console. You can pass a string as parameter as a label on the console

Python strings

Syntax	Comments
`hello = """ ... """`	Triple quotes allow you to create a multiline string
`f'Hello {name}'`	Allows you to pass the variable `name` to the string and have it parsed
`mystr.title()`	Capitalizes every word of a string
`mystr.find('str')`	Returns the index where `str` is in `mystr`
`mystr.replace('a', 'b')`	Replaces `a` to `b` in a string
`'Name' in mystr`	Returns `True` if `Name` is the string `mystr`

Basic python arithmetic

Operand	Notes
`//`	Returns an `int`
`x ** y`	`x` to the power of `y`
`x += 1`	Increment by `1`

Loops in python

Example	Notes
`for i in my_list:`	Loop trough each item of a list
`for i in range(1, 12, 3):`	Loop from 1 to 12 on an interval of 3

Python lists

Method	Notes
`.pop()`	Removes the last item
`.clear()`	Empties the list
`",".join(mylist)`	Creates a string separated by `,`
`.index('str')`	Returns the index of the first occurrence of `str`
`.copy()`	Returns a copy of the list. Useful for functional programming
`mylist[:]`	Returns a copy of the list (like above)
`mylist[:2]`	Returns from the start of the list to the 2nd item
`mylist[::-1]`	Reverse a list or string
`[x**2 for x in range(2,8)]`	List comprehension
`[x**2 for x in range(2,8) if x % 2]`	List comprehension with conditional

Dictionaries in Python

Method	Notes
`mydict.get('invalidx', 'default')`	Return the value of `mydict['invalidx']` if exits. If not, returns `default`
`for key in my_dict.keys():`	Loop trough a dictionary keys
`for key, val in my_dict.values():`	Loop trough a dictionary values
`for key, val in my_dict.items():`	Loop trough a dictionary
`{dic1, dic2}`	Merge dictionaries

Exceptions

Method	Notes
`raise Exception("desc")`	Throws a new exception
`except Exception as e:`	Catches the exception in the `e` variable
`finally:`	Allows you tu use variables declared in the `try` section

Django Cheat Sheet

Command	Action
`django-admin startproject <project_name> [path]`	Creates a new project on path (preferably `.`)
`django-admin startapp <app_name>`	Creates a new application on `app_name` path
`python manage.py runserver 0:8080`	Starts the development server
`python manage.py startapp <appname>`	Creates a new app in the project
`python manage.py makemigrations [appname]`	Creates the migration from the models
`python manage.py migrate [appname]`	Executes the migrations in the database
`python manage.py sqlmigrate [appname] [#id]`	Returns the SQL for the migration specified by `<#id>` and `<appname>`
`python manage.py shell`	Creates an interactive shell where you can import models and execute queries
`python manage.py createsuperuser`	Creates a super user

Pipenv Cheat

I've included here a list of useful pipenv commands in case you are curious.

Command	Action
`pipenv --python 3.7`	Create a project with another Python version
`pipenv install --dev`	Install packages including dev dependencies
`pipenv lock`	Burns the package versions on `Pipfile.lock` file
`pipenv clean`	Removes all packages not in `Pipfile.lock`
`pipenv run <command>`	Runs a command using the current virtualenv
`pipenv sync`	Installs the packages from `Pipfile.lock`
`pipenv uninstall`	Removes a package from the env and from the `Pipfile`
`pipenv --where`	Locates the project
`pipenv --system`	Install the packages system wide and not in a venv
`pipenv --rm`	Remove the current virtual environment
`pipenv --venv`	Locates the virtual environment
`pipenv ---py`	Locates the Python interpreter

Final notes

You can access additional Python Cheat Sheets in the SinxLooud site