Intro to Python¶

x = 3
print(type(x)) # Prints "<class 'int'>"
print(x)       # Prints "3"
print(x + 1)   # Addition; prints "4"
print(x - 1)   # Subtraction; prints "2"
print(x * 2)   # Multiplication; prints "6"
print(x ** 2)  # Exponentiation; prints "9"
x += 1
print(x)  # Prints "4"
x *= 2
print(x)  # Prints "8"
y = 2.5
print(type(y)) # Prints "<class 'float'>"
print(y, y + 1, y * 2, y ** 2) # Prints "2.5 3.5 5.0 6.25"

x = 'c'
print(type(x))

t = True
f = False
print(type(t)) # Prints "<class 'bool'>"
print(t and f) # Logical AND; prints "False"
print(t or f)  # Logical OR; prints "True"
print(not t)   # Logical NOT; prints "False"
print(t != f)  # Logical XOR; prints "True"

2 == 23

hello = 'helloworld'    # String literals can use single quotes
world = "world"    # or double quotes; it does not matter.
print(hello)       # Prints "hello"
print(len(hello))  # String length; prints "5"
hw = hello + ' ' + world  # String concatenation
print(hw)  # prints "hello world"
hw12 = '%s %s %d' % (hello, world, 12)  # sprintf style string formatting
print(hw12)  # prints "hello world 12"

s = "hello"
print(s.capitalize())  # Capitalize a string; prints "Hello"
print(s.upper())       # Convert a string to uppercase; prints "HELLO"
print(s.rjust(7))      # Right-justify a string, padding with spaces; prints "  hello"
print(s.center(7))     # Center a string, padding with spaces; prints " hello "
print(s.replace('l', '(ell)'))  # Replace all instances of one substring with another;
                                # prints "he(ell)(ell)o"
print('  world '.strip())  # Strip leading and trailing whitespace; prints "world"

xs = [3, 1, 2]    # Create a list
print(xs, xs[2])  # Prints "[3, 1, 2] 2"
print(xs[-1])     # Negative indices count from the end of the list; prints "2"
xs[2] = 'foo'     # Lists can contain elements of different types
print(xs)         # Prints "[3, 1, 'foo']"
xs.append('bar')  # Add a new element to the end of the list
print(xs)         # Prints "[3, 1, 'foo', 'bar']"
x = xs.pop()      # Remove and return the last element of the list
print(x, xs)      # Prints "bar [3, 1, 'foo']"

xs = [3, 1, 2,5,7]
xs[-len(xs)]

xs[3] = 'f'
xs

aList = [123, 'xyz', 'zara', 'abc']
aList.insert( 3, 2009)
print ("Final List : ", aList)

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]"
print(nums[2:])           # Get a slice from index 2 to the end; prints "[2, 3, 4]"
print(nums[:2])           # Get a slice from the start to index 2 (exclusive); prints "[0, 1]"
print(nums[:])            # Get a slice of the whole list; prints "[0, 1, 2, 3, 4]"
print(nums[:-1])          # Slice indices can be negative; prints "[0, 1, 2, 3]"
nums[2:4] = [8, 9]        # Assign a new sublist to a slice
print(nums) 

nums = list(range(6))  
nums

nums[:2], nums[2:4], nums[4:]

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

for animal in animals: print(animal)

animals = ['cat', 'dog', 'monkey']
for idx, animal in enumerate(animals):
    print(idx, animal)

nums = [0, 1, 2, 3, 4]
squares = []
for x in nums:
    squares.append(x ** 2)
print(squares)   # Prints [0, 1, 4, 9, 16]

nums = [0, 1, 2, 3, 4]
squares = [x ** 2 for x in nums]
print(squares)   # Prints [0, 1, 4, 9, 16]

nums = [0, 1, 2, 3, 4]
odd_squares = [x ** 2 for x in nums if x % 2 == 1]
print(odd_squares)  # Prints "[0, 4, 16]"

nums = [0, 1, 2, 3, 4]
squares = []
for x in nums:
    if x ** 2 % 2:
        squares.append(x ** 2)
squares

d = {'cat': 'cute', 'dog': 'furry'}  # Create a new dictionary with some data
print(d['cat'])       # Get an entry from a dictionary; prints "cute"
print('cat' in d)     # Check if a dictionary has a given key; prints "True"
d['fish'] = 'wet'     # Set an entry in a dictionary
d

# print(d['monkey'])  # KeyError: 'monkey' not a key of d
print(d.get('monkey'))  # Get an element with a default; prints "N/A"

d['fish']

try:
    d['monkey']
except:
    print('None')

print(d.get('monkey'))

d = {'person': 2, 'cat': 4, 'spider': 8}
for key in d.keys():
    print(key)

for val in d.values():
    print(val)

for key, val in d.items():
    print(key, val)

nums = [0, 1, 2, 3, 4]
even_num_to_square = {x: x ** 5 for x in nums}
print(even_num_to_square)

animals = {'cat', 'dog'}
print('cat' in animals)   # Check if an element is in a set; prints "True"
print('fish' in animals)  # prints "False"

A_intersect_B = {a for a in A if a in B} # set comprehension
A_intersect_B

A_intersect_B_size = len(A_intersect_B)
A_intersect_B_size

A_union_B_size = len(A) + len(B) - len(A_intersect_B)
A_union_B_size

jaccard_similarty(A,B)

t = (5, 6, 5)
t

t[2] = 9

def sign(x):
    if x > 0:
        return 'positive'
    elif x < 0:
        return 'negative'
    else:
        return 'zero'

for x in [-15, 0, 81]:
    print(sign(x))

g = Greeter('Fred')  # Construct an instance of the Greeter class
g.greet()            # Call an instance method; prints "Hello, Fred"

g.greet(loud=True)   # Call an instance method; prints "HELLO, FRED!"