University:
Boston University
Course:
GRS CS 910 | Directed Study: Systems
Academic year:

2023
Views:

329

Pages:

15
Author:

Amiah Sosa

Introduction to Python Part 2 Tutorial Outline – Part 2       Tuples and dictionaries Modules numpy and matplotlib modules Script setup Classes Development notes Tuples  Tuples are lists whose elements can’t be changed.  Like strings they are immutable  Indexing (including slice notation) is the same as with lists. Return multiple values from a function  Tuples are more useful than they might seem at first glance.  They can be easily used to return multiple values from a function.  Python syntax can automatically unpack a tuple return value. Dictionaries  Dictionaries are another basic Python data type that are tremendously useful.  Create a dictionary with a pair of curly braces: x = {}  Dictionaries store values and are indexed with keys  Create a dictionary with some initial values: x = {'a_key':55, 100:'a_value', 4.1:[5,6,7]} Dictionaries  Values can be any Python thing  Keys can be primitive types (numbers), strings, tuples, and some custom data types  Basically, any data type that is immutable  Lists and dictionaries cannot be keys but they can stored as values.  Index dictionaries via keys: x['a_key']  55 x[100]  'a_value' Try Out Dictionaries  Create a dictionary in the Python console or Spyder editor.  Add some values to it just by using a new key as an index. Can you overwrite a value?  Try x.keys() and x.values()  Try: del x[valid_key]  deletes a key/value pair from the dictionary. Tutorial Outline – Part 2       Tuples and dictionaries Modules numpy and matplotlib modules Script setup Classes Development notes Modules  Python modules, aka libraries or packages, add functionality to the core Python language.  The Python Standard Library provides a very wide assortment of functions and data structures.  Check out their Brief Tour for a quick intro.  Distributions like Anaconda provides dozens or hundreds more  You can write your own libraries or install your own. PyPI  The Python Package Index is a central repository for Python software.  Mostly but not always written in Python.  A tool, pip, can be used to install packages from it into your Python setup.  Anaconda provides a similar tool called conda  You should always do your due diligence when using software from a place like PyPI. Make sure it does what you think it’s doing! Python Modules on the SCC  Python modules should not be confused with the SCC module command.  For the SCC there are instructions on how to install Python software for your account or project.  Many SCC modules provide Python packages as well.  Example: tensorflow, pyopencl, others. Importing modules  The import command is used to load a module.  The name of the module is prepended to function names and data structures in the module.  The preserves the module namespace  This allows different modules to have the same function names – when loaded the module name keeps them separate. Fun with import  The import command can strip away the module name: from math import *  Or it can import just a single function: from math import cos  Or rename on the import: from math import sin as exact_sin Fun with import  The import command can also load your own Python files.  The Python file to the right can be used in another Python script: # Don't use the .py ending import myfuncs x = [1,2,3,4] y = myfuncs.get_odds(x) myfuncs.py def get_odds(lst): ''' Gets the odd numbers in a list. lst: incoming list of integers return: list of odd integers ''' odds = [] for elem in lst: # Odd if there's a remainder when # dividing by 2. if elem % 2 != 0: odds.append(elem) return odds Import details  Python reads and executes a file when the file  is opened directly: python somefile.py  is imported: import somefile  Lines that create variables, call functions, etc. are all executed.  Here these lines will run when it’s imported into another script! myfuncs.py def get_odds(lst): ''' Gets the odd numbers in a list. lst: incoming list of integers return: list of odd integers ''' odds = [] for elem in lst: # Odd if there's a remainder when # dividing by 2. if elem % 2 != 0: odds.append(elem) return odds x = [1,2,3,4] y = get_odds(x) print(y)