August 10, 2020
Read Time: 6 mins

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.



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


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 runserver 0:8080 Starts the development server
python startapp <appname> Creates a new app in the project
python makemigrations [appname] Creates the migration from the models
python migrate [appname] Executes the migrations in the database
python sqlmigrate [appname] [#id] Returns the SQL for the migration specified by <#id> and <appname>
python shell Creates an interactive shell where you can import models and execute queries
python 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