import sys print('Hello, World') print("It's raining!") print(''' Welcome to Python Have a great day!!! ''') a = None print(a) 

x = 25 # integer y = 17.0 # float  print(x) print(y) print(x + y) print(x - y) print(x * y) print(x / y) print(x // y) # integer division  print(x % y) # modulo  print(f'The result is {int(x // y)} remainder {int(x % y)}') print(x ** 2) print(y ** 2) x = 25 y = 17.6 

 print(x * y) print(int(x * y)) print(round(x * y, 2)) 

print(int(17.2)) print(int(17.9)) 

name = input('What is your name?\n') print('Hi, ' + name + '.') print('Hi, %s.' % name) print('Hi, {fname} {lname}.'.format(lname="Doe", fname="John")) print(f'Hi, {name}.') 

a = False try: print(len(a)) except: print(f'{a} has no length') 

# More complex try blocks  a = 'False' b = 6 c = 2 try: print(len(a)) print(b/c) print(a[47]) except TypeError: print(f'{a} has no length') except ZeroDivisionError as err: print(f'Cannot divide by zero! Error: {err}') except: print(f'Uh oh, unknown error: {sys.exc_info()}') else: print('No errors! Nice!') finally: print('Thanks for using the program!') # Arithmetic with Strings  a = "a" b = "b" an = "an" print(b + an) print(b + a*7) print(b + an*2 + a) print("$1" + ",000"*3) # Length of a string print(len("Spaghetti")) # => 9  # Indexing into strings print("Spaghetti"[0]) # => S print("Spaghetti"[4]) # => h print("Spaghetti"[-1]) # => i print("Spaghetti"[-4]) # => e  # Indexing with ranges print("Spaghetti"[1:4]) # => pag print("Spaghetti"[4:-1]) # => hett print("Spaghetti"[4:4]) # => (empty string) print("Spaghetti"[:4]) # => Spag print("Spaghetti"[:-1]) # => Spaghett print("Spaghetti"[1:]) # => paghetti print("Spaghetti"[-4:]) # => etti  # Using invalid indices # print("Spaghetti"[15]) # => IndexError: string index out of range # print("Spaghetti"[-15]) # => IndexError: string index out of range print("Spaghetti"[:15]) # => Spaghetti print("Spaghetti"[15:]) # => (empty string) print("Spaghetti"[-15:]) # => Spaghetti print("Spaghetti"[:-15]) # => (empty string) print("Spaghetti"[15:20]) # => (empty string)  # .index() function # Returns the first index where the character is found print("Spaghetti".index("t")) # => 6 # print("Spaghetti".index("s")) # => ValueError: substring not found  # .count() function # Returns the number of times the substring is found print("Spaghetti".count("h")) # => 1 print("Spaghetti".count("t")) # => 2 print("Spaghetti".count("s")) # => 0  # .split() function # Returns a list (array) of substrings, split on the character passed # If no character is passed, a space is used to split on print("Hello World".split()) # => ["Hello", "World"] print("i-am-a-dog".split("-")) # => ["i", "am", "a", "dog"]  # .join() function # Works in reverse from what you may be used to with JavaScript # Called on a string that should be used to join each substring from the passed list print(" ".join(["Hello", "World"])) # => "Hello World" # ["Hello", "World"].join(" ") JavaScript print("-".join(["i", "am", "a", "dog"])) # => "i-am-a-dog"  # .upper() and .lower() transformation functions # These functions do not mutate a = 'Hello' print(a) print(a.upper()) print(a) # Some testing methods # islower() # isupper() # startswith("substring") # endswith("substring") # isalpha() - only letters # isalnum() - letters and numbers # isdecimal() - only numbers # isspace() - only whitespace # istitle() - only title-cased letters (does not account for special words like 'a') print('Once Upon A Time'.istitle()) # => True print('Once Upon a Time'.istitle()) # => False # Assignment Operators in Python # - Increment (no postfix/prefix) # - Powers and Integer division # - Big Numbers # - Stopping a runaway process (control+c)  i = 1 # i++ does not exist in Python, we have to use i += 1 i += 1 print(i) # > 2  i += 4 print(i) # > 6  i **= 2 print(i) # > 36  i //= 10 print(i) # > 3  i *= 10**200 print(i) # > 3 followed by 200 0s (all written out)  print(float(i)) # > 3e+200 (floats are written in scientific notation)  i = 3 i **= 10**200 print(i) # runaway process! control+c triggers a KeyboardInterrupt to stop it  # Meaning of Truth in Python # - numeric types equivalent, but not strings # - conditionals (if, elif, else) # - truth equivalence  a = 1 b = 1.0 c = "1" # print(a == b) # print(a == c) # print(b == c)  # if (a == c): # print("match") # elif (a == b): # print("a matches b") # else: # print("not a match")  a = [] # Falsy Values: # 0, 0.0, 0j (complex number) # '' # False # None # [] # () # {} # set() # range(0)  if (a): print(f'{a} is true') else: print(f'{a} is false') # Logical Operators # We use the keywords 'and', 'or', and 'not' in Python instead of &&, ||, and ! print(True and False) # > False print(True or False) # > True print(True and not False) # > True  # Grouping Conditions # Parentheses can group our conditions, just like JavaScript print(False and (True or True)) # > False print((False and True) or True) # > True  # Short Circuiting # If we can already determine the overall outcome of a compound conditional # Python will not bother evaluating the rest of the statement # False and (anything else) is always False, so the print is not evaluated False and print("not printed") # Cannot determine overall value so we have to evaluate the right side False or print("printed #1") # Cannot determine overall value so we have to evaluate the right side True and print("printed #2") # True or (anything else) is always True, so the print is not evaluated True or print("not printed") # JavaScript use case of short circuiting # const composeEnhancers = window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose; # While loops follow a very similar structure to JavaScript i = 0 while i < 5: print(f'{i+1}. Hello, world.') i += 1 # The 'continue' keyword goes to the next loop # The 'break' keyword exits out of the loop completely i = 0 while True: print(f'{i+1}. Hello, world.') if i < 4: i += 1 continue print("You've printed 5 times. Goodbye.") break # Identity vs. Equality # - is vs. == # - working with literals # - isinstance()  a = 1 b = 1.0 c = "1" print(a == b) print(a is b) print(c == "1") print(c is "1") print(b == 1) print(b is 1) print(b == 1 and isinstance(b, int)) print(a == 1 and isinstance(a, int)) # d = 100000000000000000000000000000000 d = float(10) e = float(10) print(id(d)) print(id(e)) print(d == e) print(d is e) b = int(b) print(b) print(b == 1 and isinstance(b, int)) print(a) print(float(a)) print(str(a)) print(str(a) is c) print(str(a) == c) # Make an xor function # Truth table # | left | right | Result | # |-------|-------|--------| # | True | True | False | # | True | False | True | # | False | True | True | # | False | False | False | # def xor(left, right): # return left != right  def xor(left, right): return left != right print(xor(True, True)) # > False print(xor(True, False)) # > True print(xor(False, True)) # > True print(xor(False, False)) # > False  def print_powers_of(base, exp=1): i = 1 while i <= exp: print(base ** i) i += 1 # We are not hoisting the function declaration, we need to invoke after declared print_powers_of(15) print_powers_of(exp=6, base=7) print_powers_of(2, 5) print_powers_of(3, 5) print_powers_of(10, 5) if True: x = 10 print(x) print(i) def greeting_maker(salutation): print(salutation) def greeting(name): return f"{salutation} {name}" return greeting # print(salutation) # Error, salutation is not defined at this scope  hello = greeting_maker("Hello") hiya = greeting_maker("Hiya") print(hello("Monica")) print(hello("Raja")) print(hiya("Raul")) print(hiya("Tariq")) 

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