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https://github.com/nemanjam/python-overview

Python language overview.
https://github.com/nemanjam/python-overview

cheatsheet python

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Python language overview.

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README 

          
# Python language overview



Notes from [_"Core Python learning path"_](https://www.pluralsight.com/paths/core-python) - on Pluralsight.



- _"Big Picture"_ - by Jason Olson

- _"Core Python 3: Getting-Started"_

- _"Python 3: Beyond the Basics"_

- _"Advanced Python"_ - all 3 by Austin Bingham and Robert Smallshire

- _"Managing Python Packages and Virtual Environments"_

- _"Python Best Practices for Code Quality"_ - by Reindert-Jan Ekker



---



### Big Picture



#### Why Python?



#### What is Python?



Python is general purpose, multi-paradigm, interpreted, garbage collected, dynamically typed language with comprehensive standard library, 



#### Python Pros and Cons



---



### Getting Started



#### Installing and Starting Python



#### Scalar Types, Operators, and Control Flow



_scalar types_ - all immutable, int, float, None, bool, _control flow_ - if, else, elif, _loops_ - while, for, _relational operators_, _and, or, not_ - logical operators, _in_ - membership operator, _is_ - identity operator, 



#### Introducing Strings, Collections, and Iteration



_str_ - immutable string type and literals, _bytes_ - binary type, encoding and literals, 



#### Modularity



_modules_ - .py files, _\_\_name\_\_ attribute_ - detect if file is imported or executed in shell, _python execution model_ - function name is bound to definition at runtime, _sys.argv[...]_ - passing command line arguments, _main()_ - custom entry point for a python script, _shebang_ - run python file as shell script, _docstrings_ - singleline and multiline, 



#### Objects and Types



_object and type models_, _identity equality_ - defined on language level, _value equality_ - defined on type level, _all variables are references, not boxes_ - all variables including scalar types, _pass by reference_ - arguments and return values, _positional and keyword arguments_ - defined on invocation, _default arguments_ - called at bind time, must be immutable types, _strong, dynamic type system_ - types resolved at runtime,  no type coercion to match type, _4 levels scope - LEGB_ - local, enclosing, global, built in, _everything is an object_ - including scalar types, functions and modules, 



#### Built-in Collections



_built in collections_, _list [...]_ - mutable, indexed, ordered collection with duplicates, _tuple (...)_ - immutable, indexed, ordered collection with duplicates, _ranges_ - arithmetic progression of integers, _dictionary {key: val}_ - unordered, indexed, mutable collection without duplicates - associative array - JavaScript object equivalent, _set {...}_ - unordered, non-indexed, mutable collection of immutable elements without duplicates, _protocols_ - set of functions, interface, 



#### Exceptions



_try, except_ - exception handling, _raise_ - throwing exceptions, _finally_ - block for cleanup actions, _programmer errors_ - should not be handled, _exceptions are part of the function signature and protocols_, _EAFP_ - easier to ask forgiveness than permission - try catch, can not be ignored, _LBYL_ - look before you leap - if else without exception, error codes, silent,



#### Iteration and Iterables



_comprehensions_ - concise syntax to transform collections without side effects - consists of expression, for loop and optional predicate, _generator functions_ - iterables defined via functions, have yield keyword, evaluated lazily, can model infinite sequences, can maintain state in local variables, _iteration protocols_ - iter() and next(), _generator expressions_ - create generator objects  with comprehensions, use (...) braces, _itertools_ - module for working with iterators, 



#### Classes



_classes_ - custom types, classes are callable objects in Python, name bound to definition once at runtime, PascalCase naming, no new keyword, _self_ - equivalent to this in Java, simply assign class attributes without declaration, _\_\_init\_\_()_ - initializer, not a constructor, for configuring already created object, _methods_ - first argument is self and passed explicitly, _no access modifiers_ - everything is public, underscore for private attributes, _invariants_ - constraints, validate attributes, _duck typing_ - argument fitness determined at runtime, not by inheritance hierarchy at compile time, _late binding_ - use object to resolve method calling at runtime, _polymorphism_ - through late binding, not through inheritance, _inheritance_ - used only for reusing implementation, 



#### File IO and Resource Managements



_files and file like objects_ - text and binary mode, support iterator and context manager protocols, _universal newline_ - OS independent, _bitwise operators_, _with block_ - syntactic sugar for try except structure for managing resources using objects that implement context manager protocol, 



---



### Beyond the Basics



#### Organizing Larger Programs



_packages_ - folders, _modules_ - files, _sys.path_ - list of all included directories with modules, _PYTHONPATH_ - OS level environment variable that is included in sys.path, _\_\_init\_\_.py_ - index file that creates  a package from a folder, _subpackages_ - package can have hierarchy, _relative imports_ - from import syntax with a dot, _\_\_all\_\__ - export only some variables from a module, _namespace packages_ - package composed from a few sibling folders, _\_\_main\_\_.py_ - create executable directories, _recommended layout_ - recommended folder structure with source, test, index and setup files, _module singletons_ - variables defined in modules are singletons, 



#### Beyond Basic Functions



_positional and keyword arguments_ - determined in the function call, _default arguments_ - evaluated only once at import time, must not be mutable value, _callable instances_ - their class has \_\_call\_\_() method defined, used as stateful functions, _callables_ - functions, classes, callable objects, lambdas, _conditional expressions_ - ternary expression equivalent, _lambdas_ - single expression anonymous functions, _extended formal and actual arguments syntax_ - def fn(\*args, \*\*kwargs), fn(\*args), fn(\*\*args) - equivalent to rest and spread syntax in JavaScript, unpacking - destructuring, _global functions_ - definition bound to name at runtime (import time), _local functions_ - redefined on each parent function call, _LEGB scopes_ - local, enclosing, global (module), built in, _function are first class citizens_ - can be passed, returned, assigned, _closures_ - maintain references from parent scopes, prevent garbage collection,



#### Closures and Decorators



_\_\_closure\_\__ - reference to the closure variables, _function factories_ - functions that returns new specialized functions, _nonlocal and global keywords_ - reuse variables frm parent and global scope, _decorators_ - syntactic sugar for higher oder functions, accepts callable and returns callable, can be nested, _@functools.wraps()_ - helper decorator for forwarding metadata of the decorated function, _instance attributes_ - per instance, 



#### Properties and Class Methods



_class attributes_ - per class, same for all instances, _@staticmethod_ - does not reference neither class nor self, _@classmethod_ - references only class, _@property_ - property getter, _@name.setter_ - property setter, 



#### Strings and Representations



_str()_ - simple string representation, calls \_\_str\_\_(), meant for users, called on print(), _repr()_ - verbose string representation, calls \_\_repr\_\_(), required, meant for developers, _format()_ - calls \_\_format\_\_(), optional, _ascii(), ord(), chr()_ - helpers for escaping and translating ascii to unicode strings, 



#### Numeric and Scalar Types



_int_ - unlimited precision signed integer, _float_ - 64 bits floating point, _Decimal_ - configurable finite precision decimal floating point, _Fraction_ - rational numbers, _complex()_ - complex numbers, _abs(), round()_ - built in math helpers, _bin(), oct(), hex(), int()_ - number base conversion helpers, _datetime module_ - time(), datetime(), timedelta(), timezone() for working with time, 



#### Iterables and Iteration



_advanced comprehensions_ - multiple input sequences - nested loops, if clauses, in the result expression of a comprehension - multidimensional result, _map()_ - returns iterable, lazy, _filter()_ - accepts predicate, returns iterable, lazy, _reduce()_ - summation generalization, _iter(iterable)_ - requires \_\_iter\_\_(), iterable protocol, _next(iterator)_ - requires \_\_next\_\_() and \_\_iter\_\_(), iterator protocol, _\_\_getitem\_\_()_ - iterable protocol for subsequent indexes, _iter(callable, sentinel)_ - extended iter format, 



#### Inheritance and Subtype Polymorphism



_single inheritance_, _multiple inheritance_, _isinstance() and issubclass()_ - helper methods, _method resolution order - MRO_ - search order of inheritance graph, Class.\_\_mro\_\_ and mro(), calculated by C3 algorithm, which base class method will be called, _super()_ - returns bound class or instance proxy object in class or instance methods, returns base class in single inheritance, _inheritance usage_ - not for type hierarchy but for reusing implementation, 



#### Implementing Collections



_collection protocols_ - container, sized, iterable, sequence, set, string representation and value equality protocols, _collections.abc_ - module with base implementations for collection protocols, 



#### Exceptions and Errors



_standard exception hierarchy_, _custom exceptions_ - should extend from Exception class, _implicit chaining exceptions_ - handling new exceptions in except block, \_\_context\_\_ attribute, _explicit chaining exceptions_ - raise new exceptions from except block, \_\_cause\_\_ attribute, _traceback objects_ - stack trace, print_tb() and format_tb() for printing, _asserts_ - check assumptions, raise AssertionError for False, useful for return values,



#### Defining Context Managers



_context manager_ - object used in with statement, used for unmanaged resources, _context manager protocol_ - \_\_enter\_\_(), \_\_exit\_\_() - setup, teardown methods, for creating custom context managers, _@contextlib.contextmanager_ - decorator for creating context managers, _multiple context managers_ - nested, 



#### Introspection



_introspection_ - programs can inspect their own structure and state, types, objects, scopes, _easier to ask forgiveness than permission - EAFP_ - optimistic philosophy, preferred, _look before you leap - LBYL_ - pessimistic philosophy, _dir(), getattr(), hasattr(), callable()_ - introspecting objects, _globals(), locals()_ - introspecting scopes, _inspect module_ - standard library module for introspecting objects, 



---



### Advanced Python



#### Advanced Flow Control



_while else, for else clauses_ - no-break exit from a loop, _try else clause_ - no exception block, _emulating switch statements_ - if, elif, elif, else or dictionary of functions,



#### Byte-oriented Programming



_bitwise operators_ - and, or, xor, not, left and right shift, _bin() and to_bytes()_ - convert integers to bits and bytes, _bytes type_ - immutable sequence of bytes, _bytearray type_ - mutable sequence of bytes, _reading C structures_, _memoryview, memory mapped files_ - copy free working with binary data, C buffer protocol,



##### Only short explanations bellow.



#### Object Internals and Custom Attributes



_object internal representation as dictionary_ - attributes in obj.\_\_dict\_\_, methods in obj.\_\_class\_\_.\_\_dict\_\_, 



#### Descriptors



_descriptors_ - property objects that implement descriptor protocol, getter and setter equivalent,



#### Instance Creation



_instance allocation and initialization_



#### Metaclasses



_metaclasses_ - convert class definition into a class object, customization of class creation, type of a class object, 



#### Class Decorators



_class decorators_ - simpler and less powerful metaclasses alternative, 



#### Abstract Base Classes



_abstract base classes_ - customizable with metamethods, _abc module_ - tools for ABCs, _@abstractmethod_ - prevent instantiation of incomplete subclasses, 



---



### Managing Python Packages and Virtual Environments



#### Managing Python Packages with pip



_pip_ - manage packages,



#### Setting up Your Project with Virtual Environments



_virtualenv, venv_ - isolated, per project dependencies and runtime, 



#### Using virtualenvwrapper to Make Your Life Easier



utility tool



#### Choosing the Right Tools



_pipenv, poetry_ - deterministic dependency management, 



---



### Python Best Practices for Code Quality



#### Following Python Style Guidelines: PEP8 and Pylint



_pylint, black_ - PEP8 formatting and linting,



#### Documenting Your Project



_docstrigns_, _sphinx_ - .rst to html converter, _apidoc_ - docstrings to html, 



#### Improve Your Code with Type Checking



_type hints_ - optional type information, _mypy_ - static type checking,