Code snippets in Python.

Variables

Operations

**  2**3=8
%   22%8=6
//  22//8=2
/   22/8=2.75
*   3*3=9
-   5-2=3
+   2+2=4

var += 1    =>    var = var + 1
var -= 1    =>    var = var - 1
var *= 1    =>    var = var * 1
var /= 1    =>    var = var / 1
var %= 1    =>    var = var % 1

Examples

2 + 3 * 6 # 20

(2 + 3) * 6 # 30

2 ** 8 # 256

23 // 7 # 3

23 % 7 # 2

(5 - 1) * ((7 + 1) / (3 - 1)) # 16.0

example = 'hello'
example += 'world'
example
# hello world

number = 1
number += 1
number
# 2

exampleList = ['example']
exampleList *= 4
exampleList
# ['example', 'example', 'example', 'example']

'strOne' 'strTwo' #strOnestrTwo

'strOne' * 2 # strOnestrOne

Lists

Lists store items in a particular order.

new_fruit = [] #initialise empty array

fruit = ['apple', 'pear', 'orange', 'lemon']
fruit_one = fruit[0]            # 'apple'
fruit_last = fruit[-1]          # 'lemon'
fruit[0] = 'lime'               # 'apple' is now 'lime'
fruit.append('apple')           # add 'apple' to end of list
fruit.insert(2, "plum")         # add 'plum' at position two
del fruits[0]                   # delete an element by position
fruit.remove("lemon")           # delete an element by value
fruit_pop_last = fruit.pop()    # pop last element from list
fruit_pop_first = fruit.pop(0)  # pop first element from list
no_fruits = len(fruit)          # length of list
fruit.sort()                    # sort list
fruit.sort(reverse=True)        # revse list in alphabetical order
fruit.reverse()                 # reverse order of list

Functions and Classes

Functions

def greet_user():
  ""Display a simple greeting.""
  print("Hello")
greet_user()

def greet_user(user):
  ""Display a simple greeting.""
  print("Hello, " + user + "!")
greet_user('userOne')

def greet_user(name, age=None):
  ""Display information about user.""
  print("Hello, " + user + " you are " + age + " years old!")
greet_user('userOne', 10)
greet_user('userTwo')

def get_full_name(first, last):
  ""Return a neatly formatted full name.""
  full_name = first + '' + last
  return full_name_title()
musician = get_full_name('Jimi", "Hendrix")
print(musician)

# returning a dictionary
def build_person(first, last):
  ""Return a dictionary of information about a person.""
  person = {'first': first, 'last': last}
  return person
musician = build_person("Jimi", "Hendrix")
print(musician)

# returning a dictionary with optional values
def build_person(first, last, age=None):
  ""Return a dictionary of information about a person.""
  person = {'first': first, 'last': last}
  if age:
    person['age'] = age
  return person
musician = build_person("Jimi", "Hendrix", 27)
print(musician)
musician = build_person("Janis", "Joplin")
print(musician)

# passing a list to a function
def greet_users(names):
  ""Print a simple greeting to everyone.""
  for name in names:
    msg = "Hello, " + name + "!"
    print(msg)
usernames = ['userOne', 'userTwo']
greet_users(usernames)

# passing an arbitrary number of arguments
def make_pizza(size, *toppings):
  ""Make a pizza.""
  print("\nMaking a " + size + " pizza.")
  print("Toppings:")
  for topping in toppings:
    print("- " + topping)
make_pizza('small', 'cheese')
make_pizza('medium', 'mushrooms', 'peppers')

# modules
def make_pizza(size, *toppings):
  ""Make a pizza.""
  print("\nMaking a " + size + " pizza.")
  print("Toppings:")
  for topping in toppings:
    print("- " + topping)

import pizza
pizza.make_pizza('medium', 'mushrooms')

from pizza import make_pizza
make_pizza('medium', 'mushrooms')

import pizza as p
p.make_pizza('medium', 'mushrooms')

from pizza import make_pizza as mp
mp('medium', 'mushrooms')

from pizza import *
make_pizza('medium', 'mushrooms')

Classes

class Car():
  ""A simple attempt to model a car.""
  def __init__(self, make, model, year):
    ""Initialise car attributes.""
    self.make = make
    self.model = model
    self.year = year
    self.fuel_capacity = 15
    self.fueld_level = 0
  def fill_tank(self):
    ""Fill gas tank to capacity.""
    self.fuel_level = self.fuel_capacity
    print("Fuel tank is full.")
  def drive(self):
    ""Simulate driving""
    print("The car is moving")

  my_car = Car('audi', 'a4', 2016)
  print(my_car.make)
  print(my_car.model)
  print(my_car.year)

  my_car.fill_tank()
  my_car.drive()

  my_car = Car('audi', 'a4', 2016)
  my_old_car = Car('subaru', 'outback', 2013)
  my_truck = Car('toyota', 'tocoma', 2010)

  my_new_car = Car('audi', 'a4', 2016)
  my_new_car.fuel_level = 5

  def update_fueld_level(self, new_level):
    ""Update the fuel level.""
    if new_level <= self.fuel_capacity:
      self.fuel_level = new_level
    else:
      print("The tank can't hold that much.")

  def add_fuel(self, amount):
    ""Add fuel to the tank.""
    if(self.fuel_level + amount <= self.fuel_capacity):
      self.fueld_level += amount
      print("Added fuel.")
    else:
      print("The tank won't hold that much.")

  # inheritance
  class ElectricCar(Car):
    ""A simple model of an electric car.""
    def __init__(self, make, model, year):
      ""Initalise an electric car.""
      super().__init__(make, model, year)
      self.battery_size = 70
      self.charge_battery = 0

    # adding new methods to the child class
    classElectricCar(Car):
      --snip--
      def charge(self):
        ""Fully charge the vehicle.""
        self.charge_level = 100
        print("The vehicle is fully charged.")

    # using child and parent methods
    my_ecar = EletricCar('tesla', 'mode s'. 2016)

    my_ecar.charge()
    my_ecar.drive()

# overring parent methods
class EletricCar(Car):
  --snip--
  def fill_tank(self):
    ""Display an error message.""
    print("This car has no fuel tank.")

# instance as attributes
class Battery():
  ""A battery for an eletric car.""
  def __init__(self, size=70):
    ""Initalise battery attributes.""
    self.size = size
    self.charge_level = 0
  def get_range(self):
    ""Return the battery's range.""
    if self.size == 70:
      return 240
    elseif self.size == 85:
      return 270
# using an instance as an attribute
class EletricCar(Car):
  --snip--
  def __init(self, make, model, year):
    ""Initialise an electric car.""
    super().__init__(make, model, year)
    self.battery = Battery()
  def charge(self):
    ""Fully charge the vehicle.""
    self.battery.charge_level = 100
    print("The vehicle is fully charged.")

  my_ecar = EletricCar('tesla', 'model x', 2016)
  my_ecard.charge()
  print(my_ecar.battery.get_range())
  my_ecar.drive()

  # storing classes in a file (car.py)
  ""Represent gas and eletric cars.""
  class Car():
    ""A simple attempt to model a car.""
    --snip--
  class Battery():
    ""A battery for an eletric car.""
    --snip--
  class EletricCar(Car):
    ""A simple model of an eletric car.""
    --snip--

  # importing individual classes from a module(my_cars.py)
  from car import Car, EletricCar

  my_beetle = Car('volkswagen', 'beetle', 2016)
  my_beetle.fill_tank()
  my_beetle.drive()

  my_tesla = car.EletricCar('tesla', 'model s', 2016)
  my_tesla.charge()
  my_tesla.drive()

  # importing an entire module
  import car

  my_beetle = car.Car('volkswagen', 'beetle', 2016)
  my_beetle.fill_tank()
  my_beetle.drive()

  my_tesla = car.EletricCar('tesla', 'model s', 2016)
  my_tesla.charge()
  my_tesla.drive()

  # importing all classes from a module
  from car import *
  my_beetle = Car('volkswagen', 'beetle', 2016)

  # classes should inherit from object
  class ClassName(object):

  # other examples
  class ChildclassName(Parentclass):
    def __init__(self):
      super(Classname, self).__init__()

  class EletricCar(Car):
    def __init__(self, make, model, year):
      super(EletricCar, self).__init__(make, model, year)

Dictionaries

Python dictionaries allow you to connect pieces of information. This information is stored as key-value pair. When you provide a key, Python returns the value associated with that key.

example_dict = {'colour': 'yellow', 'num': 10}
example_dict_colour = example_dict.get('colour') # 'yellow'
example_dict_num = example_dict.get('num', 0) # 10
example_dict['color'] = 'red' # modifying values
example_dict['num'] = 50

# storing key-value pairs
example_dict['x'] = 0
example_dict['y'] = 25
example_dict['another_example'] = 1.5

new_dict = {} # empty dictionary
new_dict['colour'] = 'green'
new_dict['num'] = 100

fav_colour = {
  'red': 10,
  'blue': 15,
  'green': 20
}

for colour, num in fav_colour.items():
    print(colour+ ": " + num)
# red: 10
# blue: 15
# green: 20

for colour in fav_colour.keys():
  print(colour)
# red
# blue
# green

for num in fav_colour.values():
  print(num)
# 10
# 20
# 30

fav_colour_len = len(fav_colour)

user_info = {
  'userOne': ['female', 10],
  'userTwo': ['male', 5],
  'userThree': ['female', 6],
  'userFour': ['male', 7]
}
for user, details in user_info.items():
  print(user + ": )
  for detail in details:
    print("- " + detail)

# preserve order in which keys and values are ordered (via OrderedDict())
user_info = OrderedDict()
user_info['userOne'] = [2, 4]
user_info['userTwo'] = [6, 8]
user_info['userThree'] = [10, 12]
user_info['userFour'] = [14, 16]
for user, details in user_info.items():
  print(user + ":")
  for detail in details:
    print("- " + detail)

Loops

age = 10
age == 10 # true
age == 200 # false

name = "Test"
name.lower() == "test" # true

age = 100
if age >= 100:
  print("You are older than 100 years old!")
else:
  print("You are less than 100 years old!")

users = ['one', 'two', 'three', 'four']
'one' in users # true
'five' in users # false

banned_users = ['one', 'two', 'three']
user = 'who'
if user not in banned_users:
  print("You can play!")

pets = ['dog', 'cat', 'dog', 'fish', 'cat', 'rabbit', 'cat']
print(pets)
while 'cat' in pets:
  pets.remove('cat')
print(pets)

Files

# reading from an entire file
filename = 'example.txt'

with open(filename) as f_obj:
  contents = f_obj.read()

print(contents)

# reading line by line
filename = 'example.txt'

with open(filename) as f_obj:
  for line in f_obj:
    print(line.rstrip())

# storing lines as a list
filename = 'example.txt'

with open(filename) as f_obj:
  lines = f.obj.readlines()

for line in lines:
  print(line.rstrip())

# writing an empty file
filename = 'example.txt'

with open(filename, 'w') as f:
  f.write("Example text")

# writing multiple lines to an empty file
filename = 'example.txt'

with open(filename, 'w') as f:
  f.write("Here is some text!\n")
  f.write("Here is another line of text.\n")

# appending to a file
filename = "example.txt"

with open(filename, 'a') as f:
  f.write("There's more...\n")
  f.write("See, I told you. \n")

# opening a file from a subfolder
f_path = 'text_files/example.txt'

with open(f_path) as f_obj:
  lines = f_obj.readlines()

for line in lines:
  print(line.rstrip())

# opening a file using an absolute path
f_path = 'home/user/text_files/example.txt'

with open(f_path) as f_obj:
  lines = f_obj.readlines()

# store data with json
""Store some numbers.""

import json

numbers = [1, 2, 3, 4, 5]

filename = 'numbers.json'
with open(filename, 'w') as f_obj:
  json.dump(numbers, f_obj)

# read json file
""Load previously stored numbers""

import json

filename = 'numbers.json'
with open(filename) as f_obj:
  numbers = json.load(f_obj)

print(numbers )