Table of Contents
- Lists
- Dictionaries
- Other Data Structures
- Conditionals
- Testing
- Importing & Packages
- Flask
- Pythonic Code
shopping = ["bread", "milk", "apple", "banana", "weetbix"]
# For range loop (You CANNOT edit the shopping list directly with item = "Goose" in the loop)
for item in shopping:
print(item)
# Traditional loop with index variable (You CAN edit the shopping list directly with shopping[i] = "Goose")
for i in range(len(shopping)):
print(shopping[i])
# Loop with both the index and element available
for i, item in enumerate(shopping):
print(f"Index: {i}, Item: {item}")
# While loops
i = 0
while i < len(shopping):
print(shopping[i])
i += 1 # There's no i++ in PythonA powerful extension on 'indexing' a list
output = [0, 1, 2, 3, 4, 5]
output[-1] # Will retrieve the last element -> 5
output[::-1] # Will reverse the list -> [5, 4, 3, 2, 1, 0]
output[2:5] # Inclusive of the 2nd index, but exclusive of the 5th index -> [2, 3, 4]
output[2:] # Will include index values from 2 until the end -> [2, 3, 4, 5]
output[:4] # Will include first 4 elements -> [0, 1, 2, 3]
output[-3:] # Will include last 3 elements -> [3, 4, 5]
output[:99] # Python figures out you don't have 99 elements -> [0, 1, 2, 3, 4, 5]The structure of list comprehension will usually be [EXPRESSION - FOR RANGE LOOP - CONDITIONAL]
'''
Copying a list
'''
pokedex = ["Bulbasaur", "Charmander", "Squirtle", "Pikachu"]
# Method 1 - For range loop and append
pokedex_copy = []
for pokemon in pokedex:
pokedex_copy.append(pokemon)
# Method 2 - Basic List Comprehension
pokedex_copy = [pokemon for pokemon in pokedex]
'''
Filtering a list with an if statement into a new list
'''
cards = [1, 2, 3, 4, 5, 6, 7, 8 , 9, 10, "Jack", "Queen", "King"]
# Method 1 - For range loop with an if statement
royal_cards = []
for card in cards:
if isinstance(card, str):
royal_cards.append(card)
# Method 2 - Conditional List Comprehension
royal_cards = [card for card in cards if isinstance(card, str)]
'''
Taking an expression over list elements into a list
'''
numbers = [1, 2, 3, 4, 5]
# Method 1 - For range loop with an expression
squares = []
for num in numbers:
squares.append(num * num)
# Method 2 - Expression inside List Comprehension
squares = [(num * num) for num in numbers]
'''
Combining Expression and Conditionals
'''
numbers = [1, 2, 3, 4, 5]
# Method 1 - For range loop with an expression
even_squares = []
for num in numbers:
if num % 2 == 0:
squares.append(num * num)
# Method 2 - Expression inside List Comprehension
even_squares = [(num * num) for num in numbers if num % 2 == 0]Similar to arrays in C, except their size is dynamic and you can have potentially different types.
NOTE: Most of these list functions return None and modify the list in place (e.g. wacky_list.reverse() returns None and reverses the list directly).
wacky_list = ["goose", "duck", True, 5, None, 4.2]
# Indexing and assigning
wacky_list[2] = False # ["goose", "duck", False, 5, None, 4.2]
# len - Extracting the element length of a list
length = len(wacky_list) # length = 6
# append - Adding a new element to the end of a list
wacky_list.append("duck") # ["goose", "duck", False, 5, None, 4.2, "Duck"]
# count -Count the occurrences of an element in a list
duck_count = wacky_list.count("duck") # duck_count = 2
# index - Retrieve the index of the first occurrences of a value
duck_index = wacky_list.index("duck") # duck_index = 1
# You can also add an optional start and end index range
duck_index = wacky_list.index("duck", 2) # duck_index = 6
duck_index = wacky_list.index("duck", 3, 6) # duck_index = 6
# NOTE: A ValueError is raised if the value is not present in the list (or in the given range)
# insert - You can insert an element at a given index, which shifts existing elements to the right
wacky_list.insert(2, "swan") # ["goose", "duck", "swan", False, 5, None, 4.2, "Duck"]
# pop - Pop will retrieve and remove a value at a given index
last_element = wacky_list.pop() # No argument will grab the last element -> "Duck"
index_element = wacky_list.pop(2) # Retrieves and removes wacky_list[2] -> "swan"
# ["goose", "duck", False, 5, None, 4.2]
# NOTE: An IndexError is raised if the list is empty, or index is out of bounds
# reverse - Reverse will mirror the list in place
wacky_list.reverse() # [4.2, None, 5, False, "duck", "goose"]
# remove - Remove the first matching element from a list
wacky_list.remove(5) # [4.2, None, False, "duck", "goose"]
# NOTE: A ValueError is raised if the element is not present in the list
# clear - Clears the list
wacky_list.clear() # wacky_list is now == []# If you have a single layer list of non-container values, you don't need to worry about references
colours = ['red', 'green', 'blue']
colours_copy = colours.copy()
# Perform a shallow copy (it will copy each sub list as a reference/pointer)
shallow_a = [['r', 'g', 'b'], ['c', 'm', 'y', 'k']]
shallow_b = shallow_a.copy()
shallow_a[0][0] = 'Red' # Will update both shallow_a and shallow_b
# shallow_b == [['Red', 'g', 'b'], ['c', 'm', 'y', 'k']]
shallow_b[0][1] = "Green" # Will update both shallow_b and shallow_a
# shallow_a == [['Red', 'Green, 'b'], ['c', 'm', 'y', 'k']]
# Perform a deep copy
import copy
deep_a = [['r', 'g', 'b'], ['c', 'm', 'y', 'k']]
# Perform a deep copy (it will copy each sub list as unique elements not references)
deep_b = copy.deepcopy(deep_a)
deep_a[0][0] = 'Red' # Will update only deep_a
deep_b[0][1] = "Green" # Will update only deep_b
# deep_a == [['Red', 'g, 'b'], ['c', 'm', 'y', 'k']]
# deep_b == [['r', 'Green, 'b'], ['c', 'm', 'y', 'k']]numbers = [1, 2]
# Extend will add the string_num list to the end of the numbers list
string_nums = ["3", "4"]
numbers.extend(string_nums) # numbers == [1, 2, '3', '4']
# The += operator can be used also
tup_nums = (5.0, 6.0)
numbers += tup_nums # numbers == [1, 2, '3', '4', 5.0, 6.0]
# List slicing the end of the list can be used as well
set_nums = {7, 8, 9}
numbers[len(numbers):] = set_nums # numbers == [1, 2, '3', '4', 5.0, 6.0, 8, 9, 7]Similar to structs from C, there are key value 'pairs' of (potentially) different data types
# Initialising a dictionary
tutors = dict()
tutors_alternative = {}
# Populating a dictionary
tutors["Yasmin"] = "W17A" # Using a string as a key (Key is "Yasmin", value is "W17A")
fav_tutor = "Sean"
tutors[fav_tutor] = "F11A" # Using a variable of a string as a key
# Defining an entire dictionary
lab_assistants = {"Miguel": "F11A", "Sean": "W17A"}
# You can also mix up data types in a dictionary
comp1531_teaching = {
"tutors": ["Sean", "Yasmin", "Nick"], # A string key and list value
"lab_assistants": lab_assistants, # A string key and a value of a dictionary
2021: True, # An integer key, with a boolean value
1.5: None # A float key, with a None value
}Looping through dictionaries we need to be aware of both the key and/or value.
comp1531_f11a_class = {
"Groups": ["ALPACA", "BEAGLE", "CAMEL", "DODO", "EAGLE"],
"Team Names": ["Throne Trouble", "Celery Creature", "Pig Partner", "Sun Surprise", "Waste Wish"],
"Tutors": ["Sean", "Miguel"]
}
# Looping over each key -> "Groups", "Team Names", "Tutors"
for key in comp1531_f11a_class.keys(): # Removing .keys() is equivalent
print(key)
# You can access the values with the key
for value in comp1531_f11a_class[key]:
print(value)
# Looping over each value -> ["ALPACA", "BEAGLE", ...], ["Throne Trouble", "Celery Creature", ...], ...
for value in comp1531_f11a_class.values():
print(value)
# Since each value of the dictionary is a list, you can loop over the individual list elements too
for value in value:
print(value)
# Looping over both key and values
for key, value in comp1531_f11a_class.items():
print(f"Key: {key}, Value: {value}")# TODO# clear()
# copy()
# fromkeys()
# get()
# items()
# keys()
# pop()
# popitem()
# setdefault()
# update()
# values()# TODO# TODORemember code blocks in python denoted by the ':' colon symbol and using indentation
weather = "Sunny"
if weather == "Sunny":
print("Wow it is a lovely day")
elif weather == "Rainy":
print("Better bring my umbrella today")
else:
print("I need to go check the weather")
# Long If Statements with brackets (Recommended)
if (weather == "Sunny" or weather == "Windy" or weather == "Cloudy" or # You can even put a comment here
weather == "Rainy"):
print("Weather is very weathery today")
# Long If Statements with backslash
# Note: Can potentially result in bad alignment and no trailing space or comment after '\' allowed
if weather == "Sunny" or weather == "Windy" or weather == "Cloudy" or \
weather == "Rainy":
print("Weather is very weathery today")Ternary Operators allow us to combine a singular if and else statement into one line.
lost_headphones = True
# Returning Method 1 (Non-ternary)
if lost_headphones:
return "Where are they?"
else:
return "In your pocket"
# Returning Method 2 (Ternary)
return "Where are they?" if lost_headphones else "In your pocket"
hand = [1, 7, "Jack", "King"]
# Assigning Method 1 (Non-ternary)
if "Queen" in hand:
win = True
else:
win = False
# Assigning Method 2 (Ternary)
win = True if "Queen" in hand else False# TODO
# simple reusable
# Markers
# Scope
# Params
# Mark# TODO
# types of exceptions
# try/except# TODO# TODO# TODO
# types of imports
# if __name__ == "__main__"# TODO
# pip3
# requirements.txt# TODO# TODO
# 3 * 'goose'
# Printing decimal places# Python functions e.g. join
# any
# all
# types# TODO
# sorting
# reverse sorting
# sorting dictionaries based on key/value# TODO# TODO# TODO# TODO# TODO