Python Tricks Steven Pineda Cortés Based on Dan Bader’s book 

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Most simple useful advice: a Comma 

Make sure you use assertions “The proper use of assertions is to inform developers about unrecoverable errors in a program”. 

Common errors with assertions 1. Don’t use it for data validation, use regular Exceptions. 2. Asserts which never fail. 

Context Managers 

Context Managers 

Context Managers, when to use? ● Safe acquisition and release of system resources. ● Avoids resource leaks and makes code easier to read. 

Underscores, Dunders and More 

String formatting 

String formatting, which to use? if strings_are_user_supplied: use = “TemplateStrings” elif PYTHON_VERSION >= 3.6: use = “Interoplation” else: use = “New style” 

Functions are first-class citizens 1. Functions are objects (everything is). 2. Functions can be stored in data structures. 3. Functions can be passed to other functions! (high-order functions). 4. Functions can be nested. 5. Functions can capture local state. 6. Objects can behave like functions. 

Functions are first-class citizens 

Functions are first-class citizens 

Lambda functions ● Shortcut for declaring small anonymous functions. ● Restricted to a single expression. ● Don’t go crazy with them 

Decorators ● Allow you to extend and modify the behavior of a callable without permanently modifying the callable itself. ● Any sufficiently generic functionality is a great candidate: ○ Logging ○ Enforcing access control and authentication ○ Instrumentation and timing functions. ○ Rate-limiting. ○ Caching. ○ More! 

Decorators 

Decorators 

*args and **kwargs ● You can create more flexible APIs with variable number of arguments. ● Essential for decorators and other wrappers. ● If we call the function with additional arguments, args will collect them as a tuple. ● Likewise, kwargs will collect extra keyword arguments as a dictionary. 

*args and **kwargs 

Argument unpacking 

“is” vs “==” 

Every class needs a __repr__ ● Python fallsback to repr if str is not defined. ● print and format use str. ● str should be readable. ● repr should be unambiguous. 

Defining your own Exceptions ● First of all, use Exceptions! ● Asking for permission instead of forgiveness. ● Custom exceptions make it clearer. ● You can use inheritance to have a hierarchy. 

Cloning objects ● Beware of shallow copying. ● Use copy module for deep copies. ● It works even for arbitrary objects 

Cloning objects, for real. 

Abstract classes ● Abstract classes are useful. ● Python is not very strict. ● We are human. ● The sooner we fail, the better. 

Abstract classes ● ABC ensures that derived classes implement methods from the base class. ● Using ABC helps avoiding bugs and makes class hierarchies easier to maintain. 

USE PEP-8 https://www.python.org/dev/peps/pep-0008/ 

Thanks!