Python Programming

Class 3

Author: Jose Miguel Arrieta R.

Parentesis

Can you open power shell?

Tuples

Additional resource: http://cs231n.github.io/python-numpy-tutorial/#python-tuples

A tuple is an (immutable) ordered list of values.

*see examples
# Create a tuple
t = (5, 6)

# Create a tuple
tuplex = 'tuple', False, 3.2, 1

Tuples Methods

Resource: https://www.programiz.com/python-programming/tuple

Only the following two methods are available.

*see more examples
my_tuple = ('a','p','p','l','e',)

# Count
# Output: 2
print(my_tuple.count('p'))

# Index
# Output: 3
print(my_tuple.index('l'))

Lists

A list is the Python equivalent of an array, but is resizable and can contain elements of different types

resources: http://cs231n.github.io/python-numpy-tutorial/#python-tuples

*see examples
xs = [3, 1, 2]    # Create a list

#See concatenate lists and methods

Lists slicing

Python provides concise syntax to access sublists; this is known as slicing

resources: http://cs231n.github.io/python-numpy-tutorial/#python-tuples

*see examples
nums = list(range(5))     # range is a built-in function that creates a list of integers
print(nums)               # Prints "[0, 1, 2, 3, 4]"
print(nums[2:4])          # Get a slice from index 2 to 4 (exclusive); prints "[2, 3]"

Lists Loops

animals = ['cat', 'dog', 'monkey']

"""
Loops: You can loop over 
the elements of a list like this
"""
for animal in animals:
    print(animal)

"""
If you want access to the index of each element within the body of a loop, 
use the built-in enumerate function
"""
for idx, animal in enumerate(animals):
    print(str(idx)+') ' +animal)

"""
Bad alternative from Java style developers, 
better use built in enumerate
"""
for i in range(0,len(animals))
	print(animal[i])

resources: http://cs231n.github.io/python-numpy-tutorial/#python-tuples

Tuples VS Lists

resources:

http://cs231n.github.io/python-numpy-tutorial/#python-tuples

http://www.diveintopython.net/native_data_types/tuples.html

https://docs.python.org/3/tutorial/datastructures.html

  • Tuples are immutable, and usually contain a heterogeneous sequence of elements.
    • ​'faster' than lists
    • 'protect' the data
  • Lists are mutable, and their elements are usually homogeneous
  • You can't add elements to a tuple. Tuples have no append or extend method.
  • You can't remove elements from a tuple. Tuples have no remove or pop method.
  • You can know if element exists in tuple and in lists.

Sets

A set is an unordered collection with

no duplicate elements. 

animals = {'cat', 'dog','cat','dog','turtle'}



*see examples

Dictionaries

A dictionary stores (key, value) pairs,

similar to a Map in Java or an object in Javascript.

resources: http://cs231n.github.io/python-numpy-tutorial/#python-tuples

# Create a new dictionary with some data
d = {'cat': 'cute', 'dog': 'furry'}

*see examples

Convert

  1. dict to list
  2. set to list
  3. list to set
#dict to lists
"""
Note: For python 2.7, python 3.x returns a 'Dictionary view objects'
"""
d = {'a': 'Jose', 'b': 'Miguel'}
d_keys = d.keys()           #Returns list of dictionary dict's keys
d_values = d.values()       #Returns list of dictionary dict's values

#set to list 
words = "Blah", "Hello"
words_list = list(words)

#List to set 
fruit = ['banana', 'orange', 'pineapple']
fruit_set = set(fruit)

Exercise 1 [List] 

  • Write a Python function named select_odds to select the odd items of a list.
  • Note: function should result a list with result.

 

#Test cases 
>>> select_odds([24,30,44,55,12])
[55]
>>> select_odds([24,30,44,55,12,3,5,6])
[55, 3, 5]
>>>

Answer 1  

def select_odds(listA):
    odd_list = []
    for number in listA:
        if number%2 != 0:        
            odd_list.append(number)
    return odd_list

Exercise 2 [Lists] 

  • Write function select_unique_values to get unique values from a list.
  • Note: result should be in a list. 
#Test cases
>>> select_unique_values([2,2,2,2,3,3,1,2,6,7,8,9,9,10])
[1, 2, 3, 6, 7, 8, 9, 10]

>>> select_unique_values(['one','two','one','two','three','one'])
['three', 'two', 'one']

Answer 2  

def select_unique_values(listA): 
    return list(set(listA))

Exercise 3 [Dict] 

  • Write  function sum_values to sum all the items in a dictionary.
#Test cases 

d = {'a': 3, 'b': 4,'c':5}

>>> sum_values(d)
12

Exercise 4 [Dict] 

  • Write function get_max_min to get the maximum and minimum values in a dictionary and return result in form of tuple.
  • Write function get_max_min_dict to get the maximum and minimum values in a dictionary and return result in form of dictionary. 
>>> d = {'a': 3, 'b': 4,'c':50,'d':1}
>>> get_max_min(d)
(50, 1)
>>> get_max_min_dict(d)
{'max': 50, 'min': 1}

*Hint:

use max() and min() 

Answer 4  


def get_max_min(dictionary): 
	maximum = max(d.values())
	minimum = min(d.values())
	return maximum,minimum

def get_max_min_dict(dictionary): 
	maximum = max(d.values())
	minimum = min(d.values())
	return {'max':maximum,'min':minimum}
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