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Chapter 04 | Code Reuse | Function and Modules

Functions

  • Python supports modularity, i.e. to break down big chunk of code into smaller, more manageable pieces called functions.
  • Functions introduces 2 new keywords: def and return.
  • Functions can accept argument data, which acts a input to the function.
  • Functions also like in general Python language are not aware of argument types.
  • Python 3 does support indicating the type of argument and return value, but this is not make to do type checking.
  • def : def is used to create a function.
def search4vowels():
    """ Display any vowel found in an asked-for word. """
    vowels = set("aeiou")
    word = input("Provide a word to search for vowels: ")
    found = vowels.intersection(set(word))
    for vowels in found:
        print(vowels)
  • def: starts with the keyword.
  • search4vowels : a meaningful name for the function.
  • () : an empty argument list.
  • : : at the end signifies a block of code is starting.
  • search4vowels() : we can invoke the function just like this.
  • """ Hello """ : triple quotes can be used to provide a documentation to Python function.
  • Python strings can be created using 3 ways.
    • '' : use single quote.
    • "" : use double quote.
    • """ : use triple quote.
      • The triple quote is called docstrings. Their main purpose is to provide documentation in Python.
      • It can span multiple lines.

PEP 8

  • Python provides best practices for formating code. It is called PEP 8.
  • PEP 8 : Python Enhancement Protocol.
  • PEP 8 is the style guide for Python code.
  • PEP 257 : Offers documentation on how to format docstring.

Function Arguments

  • Function arguments can be provided by giving argument's name within ().
  • This arguments then becomes variable in the function name.
  • Python function can take multiple arguments, we can pass multiple arguments if it is comma separated.

Boolean

  • bool : Python has a built-in function called bool, which return True or False based on the input provided.
  • If an object evaluates to 0, it is always False.
  • A empty string, and empty list and an empty dictionary all evaluate to False.
  • Python None value also evaluates to False.
  • Critically all non-empty data structure evaluates to True.

Function Return

  • return : it is a keyword with which a Python function returns value to the caller.
  • A function terminates at return statement.
  • Function can also returns multiple values, like a list. Even in python we can return a tuple
  • An empty set is represented by set() and not {} which is for a dictionary.

Annotations

  • The function we implemented till now, has no way of describing it's input parameter or the return type.
  • The best way to do it, is to put it inside the docstring.
  • Python 3 now supports annotations(type hints).
  • The function annotations are optional and are only informational.
    • def search4vowels(word: str) -> set:
  • The goal of annotations is to make it easier for the user.
  • Annotations are a documentation standard and not a type enforcement mechanism.

Bullet Points

  • Function are a name given for a group of code.
  • def keywords introduces a function.
  • triple quote strings can be used for multi line comment or for function documentation called doc string.
  • Function can accepts any number of arguments.
  • The return statement helps in returning any number of values.
  • Function annotations can be used to document the type of your function's argument and return type.

Default Arguments

  • Any arguments in a function call can be given default value, which will be used if the caller does not provide with that parameter while calling.
  • We can assign default values by
    • def search4letters(phrase: str, letters: str = "Hello") -> set:

Positional Vs Keyword Arguments.

  • We can invoke a function by using key words arguments in-place of depending on the position while passing the values.
  • The traditional way of passing arguments is called positional arguments.

Bullet Points

  • Functions help in reducing complexity of the code, by abstracting a piece of code into a function.
  • Function can be provided with default values, which is used if that value is not passed while calling the function.
  • Keywords arguments are a new way of passing values to a function. It use a key-value pair to pass the value.

Modules

  • Modules are an efficient way to distribute function.
  • A file containing a function is a module.
  • Python import statement helps in importing both standard modules and user defined.
  • import statement search for a modules in a search path, if the module is not present in the search path it is difficult to import it.

Module Import

  • Python import statement search for a module in these path.
    • The current working directory.
    • The interpreter's site-packages directory.
    • The standard library location.
  • Create a folder and create a python file with the name vsearch.py
    • cd to that folder and, open python terminal and give import vsearch. The module is imported.
  • If we change the folder, there will be import error.
  • Python import statement does not take path to a file.

Site-packages

  • setuptools is used to install site-packages.
    • It creates a distribution description.
      • This needs creation of 2 files setup.py and README.txt
    • Generate a distribution file.
    • Install the distribution file.
  • Process to create a distribution packages.
    • Go to the modules directory.
    • Give this command based on the operation system
      • Windows
        • py -3 setup.py sdist
      • Linux
        • python setup.py sdist
      • The setup.py is the file we created.
      • sdist: is an argument to create a distribution, the default format is .tar.gz
      • The output is a file in this path dist/vsearch-1.0.tar.gz
      • Change the directory to dist.
      • If you are using a virtual environment, activate the environment.
      • Give this command to install it in the site-packages.
        • python -m pip install vsearch-1.0.tar.gz
      • It will install the vsearch module in the site-packages, either globally or in virtual env.
      • The path of site packages are in this format.
        • .env/lib/python3.7/site-packages/vsearch.py

Bullet Points

  • A module is one or more functions saved in file.
  • We can share a module if we make sure it is available in
    • the current directory
    • the interpreter's site-packages.
  • Using setuptools, we can create a module stored in the interpreter's site-packages.

Call by Value/Call by Reference

  • We can pass a function as a value or as a reference.
    • Call by value meaning, the original variables values outside the function is not changed.
    • Call by reference meaning, the original variable values outside the function changes.
  • Python supports both based on the semantics.
  • For mutable type, it may change the original value and behave like a call by reference.
  • For immutable type, it may not change the original value and behave like a call by value.
  • Even for mutable type, how we are using the value inside the function can determine if it is call by value or reference.
    • num = num * 2, changes only local to the function
    • num.append('hello'), changes the original value in the caller.

PEP - 8

  • We can use Python modules like pytest framework and pep8 plugin to check the compliance of our code to pep8.