Strings

print(”Hello, world!”) # Double quotes

print(’Hello, world!’) # Single quotes

print(”This string is “+”awesome!”) # Concatenate

print(’\n’) # New line

print(variable_name) # Print a str variable

print(”””This string runs

multiple lines!”””) # Multi-line string

Advanced Strings

my_name = “Roger”

print(my_name[0]) # Print first letter of variable

print(my_name[-1]) # Print last letter of variable

sentence = “This is a sentence”

print(sentence[:4]) # Print the word ‘This’

print(sentence[-9:-1]) # Print the word ‘sentence’

print(sentence.split()) # Splits the variable in to separate Tuple items, with the default delimiter being a space

sentence_split = sentence.split() # Splits out the variable sentence_split

sentence_join = ‘ ‘.join(sentence_split) # Join together, using a space delimiter, all of the items in Tuple sentence_split

quote = “He said, ‘give me all your money’” # An example of the fact that you need to use single quotes and double quotes, similar to other languages, rather than being able to use all single quotes or all double quotes, or…

quote = “He said, \"give me all your money"\” # Escape the characters you want inside the string

too_much_space = “     hello     “

print(too_much_space.strip()) # Strip white space from string

print(”A” in “Apple”) # Returns True

print(”a” in “Apple”) # Returns False

letter = “a”
word = “Apple”

print(letter.lower() in word.lower() # Returns True, because we’ve lowercased everything

movie = “LOTR”

print(”My favourite movie is {}.”.format(movie) # An improvement over using the ‘+’ concatenation method, to add in the variable ‘movie’. Python now knows to place the variable ‘movie’ in to the curly braces.

Math

print(50 + 50) # Addition

print(50 - 50) # Subtraction

print(50 * 50) # Multiplication

print(50 / 50) # Division

print(50 + 50 - 50 * 50 / 50) # PEMDAS / BODMAS

print(50 ** 50) # Exponents (50 to the 50th power)

print(50 % 6) # Modulo (How many times 6 goes in to 50, Modulo is the left over number, so in this case 2)

print(50 // 6) # Divison with no leftovers (in this case, rounds to 8)

Variables & Methods

foo = “This is a variable.”

print(foo) # Print variable

print(foo.upper()) # Print variable in uppercase

print(foo.lower()) # Print variable in lowercase

print(foo.title()) # Print variable as a Title (capitalises all first letters)

print(len(foo)) # Prints the character length of a variable

bar = 30 # Integer (full number)

foobar = 3.7 # Float (decimals)

print (int(bar)) # Will print 30

print(int(foobar)) # Will print 3, as integers are full numbers only, and don’t round up

print(type(bar)) # Tells us what class/type a variable is, in this case ‘int’

print(type(foobar)) # Tells us what class/type a variable is, in this case ‘float’

age = 18

age += 1

print(age) # We’ve added 1 to the variable ‘age’, which would give us 19.

birthday = 1

age += birthday

print(age) # We’ve added 1 to the variable ‘age’, via the variable ‘birthday’, which would also give us 19.

TypeError: can only concatenate str (not “int”) to str

name = “Bob”  
age = “23”

print(”My name is “ + name + “ and I am “ + age + “ years old.”) # This will error! You cannot concatenate a string with an integer ( ‘+’ and the variable ‘age’). Instead, you need to;

print(”My name is “ + name + “ and I am “ + str(age) + “ years old.”) # We converted the integer in to a string, now it works!

print(type(variable_name)) # Confirms what class/type a variable is, such as int, bool or float.

Functions

Use indentation correctly!

Note that variables defined within a function are only available within the function.

# Define a function
def who_am_i():
  name = “Bob”
  age = “23”
  print(”My name is “ + name + “ and I am “ + str(age) + “ years old.”)

who_am_i() # Run the above function

def add_one_hundred(num): # Define a function with a variable input requirement. When we call the function, we must give it a variable to work with, of the correct type (str,int,float)

print(num + 100)

add_one_hundred(50) # Runs the above function, adding 100 to 50, giving us 150

def add(x,y): # Define a function with two input requirements. When we call the function, we must give it two variables to work with, of the correct type (str,int,float)

print (x + y) # Prints the result of x + y

add(7,10) # Runs the above function, adding 7 and 10 together, giving us 17

def multiply(x,y): # Prints the result of x * y

return x * y # Stores the output of the function for later use. The print, below, prints it out, instead of defining print on this line. Maybe we want to do something else with the output, instead of print.

print(mutiple(7,7)) # Prints the result of 7 * 7

def square_root(num) # Prints the Square Root of num

print(num ** .5) # Variable ‘num’ to the power of 0.5, which is the same as ‘the square root of’

square_root(64) # Prints the Square Root of 64

def nl(): print(’\n’) # Example of a new line function, saving us time and effort going forwards

nl() # Run the ‘new line’ function we just created above

Boolean Expressions (True / False)

Note, there is a difference between True and “True”. The first is a Boolean, the second is a String.

bool_1 = True
bool_2 = 3*3 == 9
bool_3 = False
bool_4 = 3*3 != 9

print(bool_1,bool_2,bool_3,bool_4) # Prints ‘True True False False’, because bool_2 is a True statement whereas bool_4 is a False statement.

print(type(bool_1)) # Tells us what class/type a variable is, in this case ‘bool’

print(”A” in “Apple”) # Returns True

print(”a” in “Apple”) # Returns False, because the Boolean search is case sensitive

letter = “a”
word = “Apple”

print(letter.lower() in word.lower() # Returns True, because we’ve lowercased everything

Relational & Boolean Operators (LT, GT, EQ, AND, OR, NOT)

greater_than = 7 > 5 # More than is an operator. This will return True.

less_than = 5 < 7 # Less than is also an operator. This will also return True.

great_than_equal_to = 7 >= 7 # Returns True

less_than_equal_to = 7 <= 7 # Returns True

test_and = (7 > 5) and (5 < 7) # AND Operator, returns True

test_and2 = (7 > 5) and (5 > 7) # AND Operator, returns False

test_or = (7 > 5) or (5 > 7) # OR Operator, returns True

test_not = not True # False

test_not2 = not False # True

Conditional Statements (IF, ELIF, ELSE)

Example of an IF statement;

def drink(money):
if money => 2:
  return “You’ve got yourself a drink!”
else
  return “No drink for you!”

print(drink(3)) # Call the ‘drink’ IF statement, set the input variable as 3. Will return Success

print(drink(1)) # Will return Failure

Example of an IF / ELSE statement;

def alcohol(age,money):
if (age >= 18) and (money >= 5):
  return “You’ve got yourself an alchoholic drink!”
elif (age >= 18) and (money < 5):
  return “Come back with more money!”
elif (age < 18) and (money >= 5)
  return “You’re not old enough to drink! Nice try.”
else:
  return “You’re too poor and too young!”

print(alcohol(21,5)) # Got a drink!

print(alcohol(18,3)) # Old enough, too poor!

print(alcohol(17,9)) # Too young!

Lists

Everything inside a list is called an Item.

Lists always live within square brackets [ ].

The first item in a list is zero.

If you define a range, the range stops just before the last defined item (up to, not including).

movies = [”LOTR”,”The Hobbit”,”Blood and Chrome”]

print(movies[1]) #Print the second item from a list. Remember, the first item is 0, not 1.

print(movies[1:3]) #Print items 1 and 2 from a list. Note that the list stops just before the last defined item, so this doesn’t print item 3, just up to 3.

print(movies[2:]) #Print item 2 and everything after it

print(movies[:2]) #Print items 0 and 1 from a list. In a similar way to the [1:3] above, the list stops just before the last defined item, so this doesn’t print item 2, just up to 2.

print(movies[-1]) #Print the very last item from a list using -1

print(len(movies)) #Print the number of items in a list

movies.append(”JAWS”) #Append/add to the end of a list

movies.pop() #Delete the last item in a list

movies.pop(1) #Delete item number 1 from a list

Tuples

Similar to Lists, however Lists are amendable and Tuples are not.
Tuples are more memory efficient than Lists, so basically if you need a “list” of items but have no requirement to amend it at any point, use a Tuple instead.

They use Parentheses rather than square brackets ( )

grades = (”a”,”b”,”c”,”d”)

print(grades[2])

print(grades[-1])

etc.

The same as the above Lists, but without the commands to append, pop or edit in any way.

Looping (FOR, WHILE)

vegetables = [”Avacado”,”Cucumber”,”Courgette”,”Pepper”]

for x in vegetables:
print(x)

Looping until we reach 10, adding 1 to variable ‘i’ each time

i = 1
while i < 10:
  print(i)
  i += 1    # Prints numbers 1 to 9

Importing Modules

Python has it’s own library of modules that you can import right off-the-bat. If you want to use a module that isn’t “standard”, you will need to add it to your Python Library.

Imports go directly after the shebang - #!/usr/bin/python

import sys # Import a module called sys, which is used for system functions and parameters

print(sys.version) # Now that we’ve imported the sys module, this command will print the version of Python we’re using

sys.exit() # Exit Python cleanly. Requires the sys module.

from datetime import datetime # Only import a specific command from a module, instead of the whole thing.

print(datetime.now()) # Prints the current date and time, using just the command we imported on the line above.

from datetime import datetime as dt # Imports the specific datetime command, from module datetime, but gives it the alias of dt

print(dt.now()) # Prints the current date and time

Dictionaries (Key:Value Pairs)

Uses curly braces { }

drinks = {”White Russian”: 7, “Old Fashioned”: 10, “Lemon Drop: 8} # Drink is the key, price is the value

print(drinks)

employees = {”Finance”: [”Bob,”Linda”,”Tina”], “IT”: [”Gene”,”Louise”,”Teddy”], “HR”: [”Jimmy Jr.”,”Mort”]} # Example of multiple Key:Value pairs

employees[’Legal’] = [”Mr. Frond”] # Adds a new Key:Value pair to employees

employees.update({”Sales”: [”Andie”, “Ollie”]}) # Also adds a new Key:Value pair to employees

drinks = {”White Russian”: 7, “Old Fashioned”: 10, “Lemon Drop": 8}

drinks[’White Russian’] = 8 # Change the Value of a Key

print(drinks.get(”White Russian”)) # Pull a specific Key from a dictionary

Sockets

A module called ‘socket’ can be used to establish and work with connections, via IPs and Ports.

Don’t call a file socket.py, it will cause issues because Linux will think it’s an actual socket.

!#/usr/bin/python

import socket

HOST = ‘127.0.0.1’
PORT = ‘1234’

# Define a short variable that refers to to the socket module, socket command,
# with the parameters of AF_INET (IPv4 connection related) and SOCK_STREAM
# (port usage related)
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Using the above, establish a connection to the specified host and port
s.connect((HOST,PORT))

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