Difference between revisions of "Python"

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# Boolean variables can only contain one of two values: True or False
#     Boolean values are annotated by using the "bool" keyword
a: bool = True
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# Integers are variables that contain any positive or negative whole number
#     Integers are annotated using the "int" keyword
# Floats are variables that contains any positive or negative decimal
#     Floats are annotated using the "float" keyword
a: int = 15
b: int = -23
 
c: float = 6.4
d: float = -9.5
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# Strings are variables that contain text
#     Strings are annotated using the "str" keyword
a: str = "This is a string"
b: str = 'Strings can be enclosed using single quotes'
 
# Initializing an empty string:
a = ""
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# Lists are collections of other variables
#     Lists are annotated using the "list" keyword
a: list = ["Some string", 15, 9.6, True]
 
# Initializing an empty list:
a = []
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# Sets are lists that cannot contain duplicate values
# They also do not keep the order of the variables
# Sets are a lot faster than lists when looking for specific values
#    Sets are annotated using the "set" keyword
a: set = {"Some string", 15, 9.6, True}
 
# Initializing an empty set:
a = set()
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# Tuples are lists that cannot be changed after being created
# They are useful when returning multiple values from a function
#     Tuples are annotated using the "tuple" keyword
a: tuple = ("Some string", 15, 9.6, True)
 
# Because tuples cannot be changed there is no point in initializing an empty one
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# Dictionaries work of Key - Value pairs
# Keys can be any immutable type - integers, floats, strings and tuples
# Dictionaries do not keep the their order
#     Dictionaries are annotated using the "dict" keyword
a: dict = {"A": "Some string", "B": 15, "C": 9.6, "D": True}
 
# Initializing an empty dictionary:
a = {}
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# Only certain operations can be performed on certain types of variables
# Changing between types of variables is called "casting"
a: str = "15"
 
b: int = int(a)     # b = 15
c: float = float(b) # c = 15.0
d: str = str(c)     # d = "15.0"

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# Integers and floats support most arithmetic operations
a = 15
b = 6
 
c = a + b # c = 21
c = a - b # c = 9
c = a * b # c = 90
c = a / b # c = 2.5
 
# There are some special operators:
# modulus (%) returns what is left after division
# floor division (//) throws away the decimal place
c = a % b  # c = 3
c = a // b # c = 2
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# Strings only support 2 mathematical operators
# The addition (+) is used to concatenate strings
# The multiplication (*) returns multiples of a string
a = "Hello"
b = "World"
 
c = a + b # c = "HelloWorld"
c = a * 3 # c = "HelloHelloHello"
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# Lists, tuples can be added to each other
# It concatenates the collections together
a = ["Hello", 15]
b = [9.6, True]
 
c = a + b # c = ["hello", 15, 9.6, True]
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# You can use "mathematical shorthand" to make some code more readable
# Shorthand is supported for all operators and works with strings, numbers, lists and tuples
a = 12
b = "Hello"
c = "World"
 
a = a + 6 # Normal way
a += 6    # Shorthand gives the same result
 
b = b + c # Normal way, c = "HelloWorld"
b += c    # Shorthand gives the same result
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# LISTS
# You can add values to a list by using the append() method:
a = []
 
a.append("Hello")
a.append(15)
a.append(True)
 
print(a) # a = ["Hello", 15, True]
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# SETS
# You can add values to a list by using the add() method
# A list of values can be added to a set by using the update() method
a = set()
b = [15, 9.6, True]
 
a.add("Hello")
a.update(b)
 
print(a) # a = {"Hello", 15, 9.6, True}
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# TUPLES
# Tuples cannot be added to, they do not change
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# DICTIONARIES
# You can add a new value pair by assigning the key to a value
a = {}
 
a["A"] = "Hello"
a["B"] = 15
a["C"] = 9.6
a["D"] = True
 
print(a) # a = {"A": "Hello", "B": 15, "C": 9.6, "D": True}
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# If statements are used when you want to do something when a condition is met
# The if or elif part occurs when the condition returns true
# The else part occurs when none of the previous conditions returned true
a = 12
b = 15
 
# The example below will return "Did the elif" because b > a
if a > b:
    print("Did the if")
elif b > a: # Condition returns true
    print("Did the elif")
else:
    print("Did the else")
 
# The operators available:
# > < >= <= ==
# != (not equal) can be used or the keyword "not"
 
# If you want to create more complex conditions you can make use of "and", "or" and "in"
# And requires that all conditionals return true
# Or requires that one of the conditionals return true
# In returns true if a certain value is found inside a collection
a = [15, 9, 6]
b = 6
 
if 15 in a:
    print("Found it")
 
# Would not run the code inside the if statement
if (15 in a) and (b > 9):
    print("The item is in the list and 6 > 9")
 
# Would run the code inside the if statement
if (15 in a) or (b > 9):
    print("The item is in the list or 6 > 9?")
 
# You can have calculations and function calls inside conditions:
if (15 + 2) > b:
    print("17 > 6")