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