diff --git a/Python in 90 minutes/Python in 90 minutes.py b/Python in 90 minutes/Python_in_90_minutes.py
similarity index 96%
rename from Python in 90 minutes/Python in 90 minutes.py
rename to Python in 90 minutes/Python_in_90_minutes.py
index 17d08eb5..c078e376 100644
--- a/Python in 90 minutes/Python in 90 minutes.py	
+++ b/Python in 90 minutes/Python_in_90_minutes.py	
@@ -1,596 +1,596 @@
-# INTRODUCTION TO PYTHON
-# ------------------------------------------------
-# to print, put text inside single or double quotes, inside parentheses.
-print('Hello World')
-
-# VARIABLES 
-# ------------------------------------------------
-# variables are used for temporary storage of data that may change
-# a single equals sign is the assignment operator
-age = 26
-first_name = 'Shivika'
-gpa = 3.99
-
-# here we can see three different types of data stored in variables: an integer, a string, and a float.
-# You do not have to declare the data type stored in each variable. Python does that for you.
-# You can see what type of data is in a variable using the type() function
-print(type(age))
-print(type(first_name))
-print(type(gpa))
-
-# variables are "dynamically typed" -- Python checks the type at runtime
-age = 26.2
-print(type(age))
-print(age, type(age))
-
-# variable naming tips: 
-#	naming can have letters, numbers and underscore, but cannot start with a digit
-#	some Python reserved words cannot be used
-#	use descriptive variable names
-#	Case Matters
-#	constants in all caps: PI = 3.14159
-# every Python variable is a pointer to the data stored somewhere in memory
-# get memory location of a variable using id() function
-print(id(age))
-
-# to swap variable values:
-x = 5
-y = 10
-x, y = y, x
-print('x =', x, 'y =', y)
-
-# BOOLEAN VALUES - True or False
-# ------------------------------------------------
-# These all evaluate to False: 0, 0.0, [], "", None
-# These are all True: any non-zero number, any non-empty string, list or set
-print(bool(1))    # True
-print(bool('dog'))
-print(bool(10.78))
-print(bool(0 or 1))
-
-print(bool(0))    # False
-print(bool(''))
-print(bool(0 and 1))
-
-# MATH FUNCTIONS
-# ------------------------------------------------
-# built-in arithmetic functions are: add, subtract, multiply, divide, power, integer division, and modulus (AKA: mod or remainder)
-#	+  Addition
-# 	-  Subtraction
-# 	*  Multiplication
-# 	/  Division
-# 	// Integer Division
-# 	%  Modulus (division remainder)
-# 	** Power
-x = 5 + 7
-print(x, type(x))
-x = 5 - 7
-print(x, type(x))
-x = 7 / 4
-print(x, type(x))
-x = 7 // 4
-print(x, type(x))
-x = 7 % 4
-print(x)
-x = 4 ** 3
-print(x)
-
-# x += 5 is the same as saying x = x + 5
-x = 2
-x = x + 5
-print(x)
-
-x = 2
-x += 5
-print(x)
-
-# Order of Operations
-#	1. ( )
-#	2. **
-#	3. * / // %
-#	4. + -
-#	Example: 1 + 5 ** (3 // 2) - 6 % 4 => 4
-x = 1 + 5 ** (3 // 2) - 6 % 4
-print(x)
-
-# CONSOLE INPUT
-# ------------------------------------------------
-# Get user input from the keyboard at the command prompt
-name = input('What is your name? ')
-print("Hello,", name)
-age = eval(input('How old are you? '))
-print('Age =', age, type(age))
-
-# With what we know so far we can write a program to get user input and compute the area of a triangle.
-base = eval(input('Enter the base: '))
-height = eval(input('Enter the height: '))
-area = base * height / 2
-print ('Area = ', area)
-
-# COMMENTS
-# ------------------------------------------------
-# Hash tag for single line comment
-'''
-Three sets of quotes 
-for multi-line comments
-'''
-""" double quotes work too """
-
-# IF-ELIF-ELSE STATEMENTS
-# ------------------------------------------------
-# requires a boolean expression 
-x = 69
-print(x > 50)
-print(x == 50)
-print(x != 50)
-
-my_age = 19
-print(my_age > 21)
-if my_age >= 21:
-    print("Old enough.")
-else:
-    print("Not old enough.")
-    print("Maybe next year.")
-
-score = 72
-if score > 90:
-    print('Grade: A')
-elif score > 80:
-    print('Grade: B')
-elif score > 70:
-    print('Grade: C')
-elif score > 60:
-    print('Grade: D')
-else:
-    print('Grade: F')
-	
-# can have multiple conditions in an if, using and/or
-my_age = 19
-grade = 'C'
-if my_age > 18 and grade == 'A':
-    print('I can go to the party!')
-
-# nested if statements -- both conditions must be True
-my_age = 19
-grade = 'C'
-if my_age > 18:
-    if grade == 'A':
-        print('I can go to the party!')
-
-# if ternary
-x = 10
-y = 20
-#  action/ if condition true/ else condfition false
-z = x + y if x > y else y - x
-print(z)
-# result 10
-
-
-# STRINGS
-# ------------------------------------------------
-# a string is a sequence of characters (ie. text)
-s = 'Howdy'
-print(s)
-print(len(s))
-print(s[3])
-print(s[1:3])
-t = ' dude! '
-s += t
-print(s + '|')
-print(s.strip() + '|')
-s = s.rstrip('! ')
-print(s)
-
-s = 'Howdy dude!'
-print(s.lower())
-print(s.upper()[:5])
-print(s.title())
-print(s.replace('Howdy', 'Greetings'))
-print(s)
-print(s.count('d'))
-print(s.find('w'))
-print('dud' in s)
-print('X' not in s)
-print(s.startswith('How'))
-print(s.endswith('cat'))
-print(s > 'Honk')
-print(s.isalpha())
-print(s[0:4].isalpha())
-print(s.isnumeric())
-
-print(s.split())
-print('5,7,9'.split(','))
-print('73.294'.split('.'))
-
-print(s[0], '\t', s[1], '\t', s[2])
-print(s[:s.find(' ')] + '\n' + s[s.find(' ')+1:])
-
-# LOOPS -- FOR, WHILE
-# ------------------------------------------------
-# used to iterate through the items of a string or list
-# indention is important. 
-# every statement indented from for will be executed each iteration
-s = 'Raj'
-for letter in s:
-    print(letter)
-for letter in s:
-    print(letter, end='')
-print()
-
-# if inside a for loop. indention is important.
-for pig in s:
-    if pig != 'a':
-        print(pig, end='')
-print()
-for i in range(len(s)):
-    print(i, end='')
-print()
-for i in range(len(s)):
-    print(s[i])
-for i in range(len(s)-1, -1, -1):
-    print(s[i])
-print(s[::-1])
-
-# while loops are an alternative to for loops
-# they check a boolean each iteration, and exit the loop when the bool is False
-x = 2
-while x < 5:
-    print('ha')
-    x += 1
-
-# DATA STRUCTURES
-# ------------------------------------------------
-# These functions all work on String, List, and Tuple
-
-# Indexing -- access any item in the sequence using its index
-x = 'frog'
-print (x[3])			# prints 'g'
-
-x = ['pig', 'cow', 'horse']
-print (x[1])			# prints 'cow'
-
-# Slicing -- slice out substrings, sublists, subtuples using indexes
-# [start : end+1 : step]
-x = 'computer'
-print(x[1:4])			# items 1 to 3, 'omp'
-print(x[1:6:2])			# items 1, 3, 5, 'opt'
-print(x[3:])			# items 3 to end, 'puter'
-print(x[:5])			# items 0 to 4, 'compu'
-print(x[-1])			# last item, 'r'
-print(x[-3:])			# last 3 items, 'ter'
-print(x[:-2])			# all except last 2 items, 'comput'
-
-# Adding / Concatenating -- combine 2 sequences of the same type using +
-x = 'horse' + 'shoe'
-print (x)				# prints 'horseshoe'	
-
-x = ['pig', 'cow'] + ['horse']
-print (x)				# prints ['pig', 'cow', 'horse']
-
-# Multiplying -- multiply a sequence using *
-x = 'bug' * 3
-print (x)				# prints 'bugbugbug'
-
-x = [8, 5] * 3
-print (x)				# prints [8, 5, 8, 5, 8, 5]
-
-# Checking Membership -- test whether an item is in or not in a sequence
-x = 'bug'
-print ('u' in x)		# prints True
-
-x = ['pig', 'cow', 'horse']
-print ('cow' not in x)	# prints False
-
-# Iterating	-- iterate through the items in a sequence
-x = [7, 8, 3]
-for item in x:
-	print (item * 2)	# prints 14, 16, 6
-	
-x = [7, 8, 3]
-for index, item in enumerate(x):
-	print (index, item)	# prints 0 7, 1 8, 2 3
-
-# Length -- count the number of items in a sequence
-x = 'bug'
-print (len(x))			# prints 3
-
-x = ['pig', 'cow', 'horse']
-print (len(x))			# prints 3
-
-# Minimum -- find the minimum item in a sequence lexicographically
-# alpha or numeric types, but cannot mix types
-x = 'bug'
-print (min(x))			# prints 'b' 
-
-x = ['pig', 'cow', 'horse']
-print (min(x))			# prints 'cow'
-
-# Maximum -- find the maximum item in a sequence
-# alpha or numeric types, but cannot mix types
-x = 'bug'
-print (max(x))			# prints 'u' 
-
-x = ['pig', 'cow', 'horse']
-print (max(x))			# prints 'pig'
-
-# Sum -- find the sum of items in a sequence
-# entire sequence must be numeric type
-x = [5, 7, 'bug']
-print (sum(x))			# error!
-
-x = [2, 5, 8, 12]
-print (sum(x))			# prints 27
-print (sum(x[-2:])) 	# prints 20	
-
-# Sorting -- returns a new list of items in sorted order
-# sorted does not change the original list
-x = 'bug'
-print (sorted(x))		# prints ['b', 'g', 'u']
-
-x = ['pig', 'cow', 'horse']
-print (sorted(x))	    # prints ['cow', 'horse', 'pig']
-
-# count (item)	
-# Returns count of an item
-x = 'hippo'
-print (x.count('p'))	# prints 2
-
-x = ['pig', 'cow', 'horse', 'cow']
-print (x.count('cow'))	# prints 2
-
-# index (item)	
-# Returns the index of the first occurrence of an item
-x = 'hippo'
-print (x.index('p'))	# prints 2
-
-x = ['pig', 'cow', 'horse', 'cow']
-print (x.index('cow'))	# prints 1
-
-# Unpacking	- unpack the n items of a sequence into n variables
-x = ['pig', 'cow', 'horse']
-a, b, c = x				# now a is 'pig', b is 'cow', c is 'horse'
-
-# LISTS
-# ------------------------------------------------
-# constructors – creating a new list
-x = list((1, 2, 3))		# note double parens
-x = ['a', 25, 'dog', 8.43]
-x = list(tuple1)
-
-# list creation using comprehensions
-x = [m for m in range(8)]
-# resulting list: [0, 1, 2, 3, 4, 5, 6, 7]
-x = [z**2 for z in range(10) if z>4]
-# resulting list: [25, 36, 49, 64, 81]
-
-# Delete -- delete a list or an item from a list
-x = [5, 3, 8, 6]
-del(x[1])				# [5, 8, 6]
-del(x)					# deletes list x
-
-# Append -- append an item to a list
-x = [5, 3, 8, 6]
-x.append(7)				# [5, 3, 8, 6, 7]
-
-# Extend -- append an sequence to a list
-x = [5, 3, 8, 6]
-y = [12, 13]
-x.extend(y)				# [5, 3, 8, 6, 7, 12, 13]
-
-# Insert -- insert an item at given index.	x.insert(index, item)
-x = [5, 3, 8, 6]
-x.insert(1, 7)			# [5, 7, 3, 8, 6]
-x.insert(1,['a','m'])	# [5, ['a', 'm'], 7, 3, 8, 6] 
-
-# Pop -- pops last item off the list, and returns item
-x = [5, 3, 8, 6]
-x.pop()					# [5, 3, 8]. and returns the 6
-print(x.pop())			# [5, 3]. and prints 8 
-
-# Remove -- remove first instance of an item
-x = [5, 3, 8, 6, 3]
-x.remove(3)				# [5, 8, 6, 3]
-
-# Reverse -- reverse the order of the list
-x = [5, 3, 8, 6]
-x.reverse()				# [6, 8, 3, 5]
-
-# Sort -- sort the list in place
-# sorted(x) returns a new sorted list without changing the original list x. 
-# x.sort() puts the items of x in sorted order (sorts in place).
-x = [5, 3, 8, 6]
-x.sort()				# [3, 5, 6, 8]
-
-# Clear	-- delete all items from the list
-x = [5, 3, 8, 6]
-x.clear()				# []
-
-# TUPLES
-# ------------------------------------------------
-# constructors – creating a new tuple
-x = ()					# no-item tuple
-x = (1,2,3)
-x = 1, 2, 3				# parenthesis are optional
-x = 2, 					# single-item tuple
-list1 = [5, 7, 7]
-x = tuple(list1)		# tuple from list
-
-# Tuples are Immutable, but member objects may be mutable
-x = (1, 2, 3)
-del(x[1])				# error!
-x[1] = 8				# error!
-
-x = ([1,2], 3)			# 2-item tuple: list and int
-del(x[0][1])			# ([1], 3)
-
-# SETS
-# ------------------------------------------------
-# constructors – creating a new set
-x = {3,5,3,5}			# {5, 3}
-x = set()				# empty set
-list1 = [5, 7, 7]
-x = set(list1)			# new set from list. strips duplicates, {5, 7}
-
-# Set Comprehension
-x = {3*x for x in range(10) if x>5} 
-# resulting set: {18, 21, 24, 27} but in random order
-
-# DICTIONARIES
-# ------------------------------------------------
-# constructors – creating a new dict
-x = {'pork':25.3, 'beef':33.8, 'chicken':22.7}
-x = dict([('pork', 25.3),('beef', 33.8),('chicken', 22.7)])
-x = dict(pork=25.3, beef=33.8, chicken=22.7)
-
-# Accessing keys and values in a dict
-x.keys()				# returns list of keys in x
-x.values()				# returns list of values in x
-x.items()				# returns list of key-value tuple pairs in x
-
-item in x.values()		# tests membership in x, returns boolean
-
-# Iterating a Dict
-for key in x:			# iterate keys
-    print(key, x[key])	# print all key/value pairs
-
-for k, v in x.items():	# iterate key/value pairs
-    print(k, v)			# print all key/value pairs
-
-# FUNCTIONS
-# ------------------------------------------------
-# use the def keyword to create a function
-# give the function a name, followed by parentheses and a colon
-# you can pass in 0 or more variables. here we pass in num.
-# you can return 0 or more variables. here we return the cube of num
-# indention is important.
-def cuber(num):
-	num_cubed = num * num * num
-	return num_cubed
-	
-# to call the function, and pass in 5:
-cuber(5)
-
-# but if you want to assign the return value (125) to a variable,
-x = 5
-x_cubed = cuber(x)
-print(x, x_cubed)
-
-# you can set default values for parameters
-def cuber(num = 2):
-	num_cubed = num * num * num
-	return num_cubed
-	
-print(cuber())		# uses the default 2
-print(cuber(3))		# 3 overrides the default
-
-# you can pass in multiple values, and return multiple values
-# but order is important
-def solve_triangle(base, height, side1, side2, side3):
-	area = base * height / 2
-	perimeter = side1 + side2 + side3
-	return area, perimeter
-	
-area, perim = solve_triangle(3, 4, 5, 3, 4)	# b=3, h=4, s1=5, s2=3, s3=4
-print('Area:', area, ' Perimeter:', perim)
-
-# above are all called "positional arguments", and order matters
-# you can also pass in "keyword arguments" when calling a function
-a, p = solve_triangle(side1=5, side2=3, side3=4, height=4, base=3)
-print(a, p)
-
-# or use a combination of both, but positional arguments must come first
-a, p = solve_triangle(3, 4, side3=4, side2=3, side1=5)
-print(a, p)
-	
-# CLASSES & OBJECTS
-# ------------------------------------------------
-# Use classes to model real-world things. 
-# Keep related data (variables) and actions (functions) in one block of code.
-class Circle:
-	# Circle constructor -- __init__ method creates a new Circle object
-	def __init__(self, r = 1):
-		self.radius = r
-		
-	def getPerimeter(self):
-		return 2 * self.radius * 3.14
-		
-	def getArea(self):
-		return self.radius ** 2 * 3.14
-# all methods have the self parameter, which is Python's reference to the object that invoked the method
-
-# this calls the __init__ method, which creates the new Circle
-circle1 = Circle(3)		
-# you can access the circle's attributes and methods using the dot operator
-print("Radius =", circle1.radius)
-print("Perimeter =", circle1.getPerimeter())	
-
-# IMPORTS
-# ------------------------------------------------
-# Python has many many classes already written that you can use
-# To access methods and data from another class you must import it
-import math
-print(math.pi)
-
-import random
-print(random.randint(1,5))
-
-# shorter version, using as to abbreviate module name
-import math as m
-print(m.pi)
-
-import random as rd
-print(rd.randint(1,5))
-
-# import just one or two functions or constants rather than a whole module
-# easier for coding, but need to beware names don't conflict
-from math import pi
-print(pi)
-
-from random import randint, shuffle
-print(randint(1,5))
-x = ['a', 'b', 'c']
-shuffle(x)
-print(x)
-
-# can rename an imported function if you want
-x = ['a', 'b', 'c']
-from random import shuffle as sf
-sf(x)
-print(x)
-
-# can also import whole module using *
-from random import *
-print(randint(1,5))
-
-# FILE READ & WRITE
-# ------------------------------------------------
-filename = 'city_data.txt'
-
-# this opens a file handle called fin, iterates the lines of the file, and prints each line
-with open(filename) as fin:
-    for line in fin:
-        print(line)
-
-# we can grab words from a line by using split, which turns each line into a list called row
-with open(filename) as fin:
-    fin.readline()
-    for line in fin:
-        row = line.split(',')
-        print('Country:', row[1], ' City:', row[2])
-
-# use the w parameter to write to an output file
-with open('Cities.txt', 'w') as fout:
-    with open(filename) as fin:
-        fin.readline()
-        for line in fin:
-            row = line.split(',')
-            fout.write(row[2] + '\n')
-
-
-
-
-
-
-
-
-
+# INTRODUCTION TO PYTHON
+# ------------------------------------------------
+# to print, put text inside single or double quotes, inside parentheses.
+print('Hello World')
+
+# VARIABLES 
+# ------------------------------------------------
+# variables are used for temporary storage of data that may change
+# a single equals sign is the assignment operator
+age = 26
+first_name = 'Shivika'
+gpa = 3.99
+
+# here we can see three different types of data stored in variables: an integer, a string, and a float.
+# You do not have to declare the data type stored in each variable. Python does that for you.
+# You can see what type of data is in a variable using the type() function
+print(type(age))
+print(type(first_name))
+print(type(gpa))
+
+# variables are "dynamically typed" -- Python checks the type at runtime
+age = 26.2
+print(type(age))
+print(age, type(age))
+
+# variable naming tips: 
+#	naming can have letters, numbers and underscore, but cannot start with a digit
+#	some Python reserved words cannot be used
+#	use descriptive variable names
+#	Case Matters
+#	constants in all caps: PI = 3.14159
+# every Python variable is a pointer to the data stored somewhere in memory
+# get memory location of a variable using id() function
+print(id(age))
+
+# to swap variable values:
+x = 5
+y = 10
+x, y = y, x
+print('x =', x, 'y =', y)
+
+# BOOLEAN VALUES - True or False
+# ------------------------------------------------
+# These all evaluate to False: 0, 0.0, [], "", None
+# These are all True: any non-zero number, any non-empty string, list or set
+print(bool(1))    # True
+print(bool('dog'))
+print(bool(10.78))
+print(bool(0 or 1))
+
+print(bool(0))    # False
+print(bool(''))
+print(bool(0 and 1))
+
+# MATH FUNCTIONS
+# ------------------------------------------------
+# built-in arithmetic functions are: add, subtract, multiply, divide, power, integer division, and modulus (AKA: mod or remainder)
+#	+  Addition
+# 	-  Subtraction
+# 	*  Multiplication
+# 	/  Division
+# 	// Integer Division
+# 	%  Modulus (division remainder)
+# 	** Power
+x = 5 + 7
+print(x, type(x))
+x = 5 - 7
+print(x, type(x))
+x = 7 / 4
+print(x, type(x))
+x = 7 // 4
+print(x, type(x))
+x = 7 % 4
+print(x)
+x = 4 ** 3
+print(x)
+
+# x += 5 is the same as saying x = x + 5
+x = 2
+x = x + 5
+print(x)
+
+x = 2
+x += 5
+print(x)
+
+# Order of Operations
+#	1. ( )
+#	2. **
+#	3. * / // %
+#	4. + -
+#	Example: 1 + 5 ** (3 // 2) - 6 % 4 => 4
+x = 1 + 5 ** (3 // 2) - 6 % 4
+print(x)
+
+# CONSOLE INPUT
+# ------------------------------------------------
+# Get user input from the keyboard at the command prompt
+name = input('What is your name? ')
+print("Hello,", name)
+age = eval(input('How old are you? '))
+print('Age =', age, type(age))
+
+# With what we know so far we can write a program to get user input and compute the area of a triangle.
+base = eval(input('Enter the base: '))
+height = eval(input('Enter the height: '))
+area = base * height / 2
+print ('Area = ', area)
+
+# COMMENTS
+# ------------------------------------------------
+# Hash tag for single line comment
+'''
+Three sets of quotes 
+for multi-line comments
+'''
+""" double quotes work too """
+
+# IF-ELIF-ELSE STATEMENTS
+# ------------------------------------------------
+# requires a boolean expression 
+x = 69
+print(x > 50)
+print(x == 50)
+print(x != 50)
+
+my_age = 19
+print(my_age > 21)
+if my_age >= 21:
+    print("Old enough.")
+else:
+    print("Not old enough.")
+    print("Maybe next year.")
+
+score = 72
+if score > 90:
+    print('Grade: A')
+elif score > 80:
+    print('Grade: B')
+elif score > 70:
+    print('Grade: C')
+elif score > 60:
+    print('Grade: D')
+else:
+    print('Grade: F')
+	
+# can have multiple conditions in an if, using and/or
+my_age = 19
+grade = 'C'
+if my_age > 18 and grade == 'A':
+    print('I can go to the party!')
+
+# nested if statements -- both conditions must be True
+my_age = 19
+grade = 'C'
+if my_age > 18:
+    if grade == 'A':
+        print('I can go to the party!')
+
+# if ternary
+x = 10
+y = 20
+#  action/ if condition true/ else condfition false
+z = x + y if x > y else y - x
+print(z)
+# result 10
+
+
+# STRINGS
+# ------------------------------------------------
+# a string is a sequence of characters (ie. text)
+s = 'Howdy'
+print(s)
+print(len(s))
+print(s[3])
+print(s[1:3])
+t = ' dude! '
+s += t
+print(s + '|')
+print(s.strip() + '|')
+s = s.rstrip('! ')
+print(s)
+
+s = 'Howdy dude!'
+print(s.lower())
+print(s.upper()[:5])
+print(s.title())
+print(s.replace('Howdy', 'Greetings'))
+print(s)
+print(s.count('d'))
+print(s.find('w'))
+print('dud' in s)
+print('X' not in s)
+print(s.startswith('How'))
+print(s.endswith('cat'))
+print(s > 'Honk')
+print(s.isalpha())
+print(s[0:4].isalpha())
+print(s.isnumeric())
+
+print(s.split())
+print('5,7,9'.split(','))
+print('73.294'.split('.'))
+
+print(s[0], '\t', s[1], '\t', s[2])
+print(s[:s.find(' ')] + '\n' + s[s.find(' ')+1:])
+
+# LOOPS -- FOR, WHILE
+# ------------------------------------------------
+# used to iterate through the items of a string or list
+# indention is important. 
+# every statement indented from for will be executed each iteration
+s = 'Raj'
+for letter in s:
+    print(letter)
+for letter in s:
+    print(letter, end='')
+print()
+
+# if inside a for loop. indention is important.
+for pig in s:
+    if pig != 'a':
+        print(pig, end='')
+print()
+for i in range(len(s)):
+    print(i, end='')
+print()
+for i in range(len(s)):
+    print(s[i])
+for i in range(len(s)-1, -1, -1):
+    print(s[i])
+print(s[::-1])
+
+# while loops are an alternative to for loops
+# they check a boolean each iteration, and exit the loop when the bool is False
+x = 2
+while x < 5:
+    print('ha')
+    x += 1
+
+# DATA STRUCTURES
+# ------------------------------------------------
+# These functions all work on String, List, and Tuple
+
+# Indexing -- access any item in the sequence using its index
+x = 'frog'
+print (x[3])			# prints 'g'
+
+x = ['pig', 'cow', 'horse']
+print (x[1])			# prints 'cow'
+
+# Slicing -- slice out substrings, sublists, subtuples using indexes
+# [start : end+1 : step]
+x = 'computer'
+print(x[1:4])			# items 1 to 3, 'omp'
+print(x[1:6:2])			# items 1, 3, 5, 'opt'
+print(x[3:])			# items 3 to end, 'puter'
+print(x[:5])			# items 0 to 4, 'compu'
+print(x[-1])			# last item, 'r'
+print(x[-3:])			# last 3 items, 'ter'
+print(x[:-2])			# all except last 2 items, 'comput'
+
+# Adding / Concatenating -- combine 2 sequences of the same type using +
+x = 'horse' + 'shoe'
+print (x)				# prints 'horseshoe'	
+
+x = ['pig', 'cow'] + ['horse']
+print (x)				# prints ['pig', 'cow', 'horse']
+
+# Multiplying -- multiply a sequence using *
+x = 'bug' * 3
+print (x)				# prints 'bugbugbug'
+
+x = [8, 5] * 3
+print (x)				# prints [8, 5, 8, 5, 8, 5]
+
+# Checking Membership -- test whether an item is in or not in a sequence
+x = 'bug'
+print ('u' in x)		# prints True
+
+x = ['pig', 'cow', 'horse']
+print ('cow' not in x)	# prints False
+
+# Iterating	-- iterate through the items in a sequence
+x = [7, 8, 3]
+for item in x:
+	print (item * 2)	# prints 14, 16, 6
+	
+x = [7, 8, 3]
+for index, item in enumerate(x):
+	print (index, item)	# prints 0 7, 1 8, 2 3
+
+# Length -- count the number of items in a sequence
+x = 'bug'
+print (len(x))			# prints 3
+
+x = ['pig', 'cow', 'horse']
+print (len(x))			# prints 3
+
+# Minimum -- find the minimum item in a sequence lexicographically
+# alpha or numeric types, but cannot mix types
+x = 'bug'
+print (min(x))			# prints 'b' 
+
+x = ['pig', 'cow', 'horse']
+print (min(x))			# prints 'cow'
+
+# Maximum -- find the maximum item in a sequence
+# alpha or numeric types, but cannot mix types
+x = 'bug'
+print (max(x))			# prints 'u' 
+
+x = ['pig', 'cow', 'horse']
+print (max(x))			# prints 'pig'
+
+# Sum -- find the sum of items in a sequence
+# entire sequence must be numeric type
+x = [5, 7, 'bug']
+print (sum(x))			# error!
+
+x = [2, 5, 8, 12]
+print (sum(x))			# prints 27
+print (sum(x[-2:])) 	# prints 20	
+
+# Sorting -- returns a new list of items in sorted order
+# sorted does not change the original list
+x = 'bug'
+print (sorted(x))		# prints ['b', 'g', 'u']
+
+x = ['pig', 'cow', 'horse']
+print (sorted(x))	    # prints ['cow', 'horse', 'pig']
+
+# count (item)	
+# Returns count of an item
+x = 'hippo'
+print (x.count('p'))	# prints 2
+
+x = ['pig', 'cow', 'horse', 'cow']
+print (x.count('cow'))	# prints 2
+
+# index (item)	
+# Returns the index of the first occurrence of an item
+x = 'hippo'
+print (x.index('p'))	# prints 2
+
+x = ['pig', 'cow', 'horse', 'cow']
+print (x.index('cow'))	# prints 1
+
+# Unpacking	- unpack the n items of a sequence into n variables
+x = ['pig', 'cow', 'horse']
+a, b, c = x				# now a is 'pig', b is 'cow', c is 'horse'
+
+# LISTS
+# ------------------------------------------------
+# constructors – creating a new list
+x = list((1, 2, 3))		# note double parens
+x = ['a', 25, 'dog', 8.43]
+x = list(tuple1)
+
+# list creation using comprehensions
+x = [m for m in range(8)]
+# resulting list: [0, 1, 2, 3, 4, 5, 6, 7]
+x = [z**2 for z in range(10) if z>4]
+# resulting list: [25, 36, 49, 64, 81]
+
+# Delete -- delete a list or an item from a list
+x = [5, 3, 8, 6]
+del(x[1])				# [5, 8, 6]
+del(x)					# deletes list x
+
+# Append -- append an item to a list
+x = [5, 3, 8, 6]
+x.append(7)				# [5, 3, 8, 6, 7]
+
+# Extend -- append an sequence to a list
+x = [5, 3, 8, 6]
+y = [12, 13]
+x.extend(y)				# [5, 3, 8, 6, 7, 12, 13]
+
+# Insert -- insert an item at given index.	x.insert(index, item)
+x = [5, 3, 8, 6]
+x.insert(1, 7)			# [5, 7, 3, 8, 6]
+x.insert(1,['a','m'])	# [5, ['a', 'm'], 7, 3, 8, 6] 
+
+# Pop -- pops last item off the list, and returns item
+x = [5, 3, 8, 6]
+x.pop()					# [5, 3, 8]. and returns the 6
+print(x.pop())			# [5, 3]. and prints 8 
+
+# Remove -- remove first instance of an item
+x = [5, 3, 8, 6, 3]
+x.remove(3)				# [5, 8, 6, 3]
+
+# Reverse -- reverse the order of the list
+x = [5, 3, 8, 6]
+x.reverse()				# [6, 8, 3, 5]
+
+# Sort -- sort the list in place
+# sorted(x) returns a new sorted list without changing the original list x. 
+# x.sort() puts the items of x in sorted order (sorts in place).
+x = [5, 3, 8, 6]
+x.sort()				# [3, 5, 6, 8]
+
+# Clear	-- delete all items from the list
+x = [5, 3, 8, 6]
+x.clear()				# []
+
+# TUPLES
+# ------------------------------------------------
+# constructors – creating a new tuple
+x = ()					# no-item tuple
+x = (1,2,3)
+x = 1, 2, 3				# parenthesis are optional
+x = 2, 					# single-item tuple
+list1 = [5, 7, 7]
+x = tuple(list1)		# tuple from list
+
+# Tuples are Immutable, but member objects may be mutable
+x = (1, 2, 3)
+del(x[1])				# error!
+x[1] = 8				# error!
+
+x = ([1,2], 3)			# 2-item tuple: list and int
+del(x[0][1])			# ([1], 3)
+
+# SETS
+# ------------------------------------------------
+# constructors – creating a new set
+x = {3,5,3,5}			# {5, 3}
+x = set()				# empty set
+list1 = [5, 7, 7]
+x = set(list1)			# new set from list. strips duplicates, {5, 7}
+
+# Set Comprehension
+x = {3*x for x in range(10) if x>5} 
+# resulting set: {18, 21, 24, 27} but in random order
+
+# DICTIONARIES
+# ------------------------------------------------
+# constructors – creating a new dict
+x = {'pork':25.3, 'beef':33.8, 'chicken':22.7}
+x = dict([('pork', 25.3),('beef', 33.8),('chicken', 22.7)])
+x = dict(pork=25.3, beef=33.8, chicken=22.7)
+
+# Accessing keys and values in a dict
+x.keys()				# returns list of keys in x
+x.values()				# returns list of values in x
+x.items()				# returns list of key-value tuple pairs in x
+
+item in x.values()		# tests membership in x, returns boolean
+
+# Iterating a Dict
+for key in x:			# iterate keys
+    print(key, x[key])	# print all key/value pairs
+
+for k, v in x.items():	# iterate key/value pairs
+    print(k, v)			# print all key/value pairs
+
+# FUNCTIONS
+# ------------------------------------------------
+# use the def keyword to create a function
+# give the function a name, followed by parentheses and a colon
+# you can pass in 0 or more variables. here we pass in num.
+# you can return 0 or more variables. here we return the cube of num
+# indention is important.
+def cuber(num):
+	num_cubed = num * num * num
+	return num_cubed
+	
+# to call the function, and pass in 5:
+cuber(5)
+
+# but if you want to assign the return value (125) to a variable,
+x = 5
+x_cubed = cuber(x)
+print(x, x_cubed)
+
+# you can set default values for parameters
+def cuber(num = 2):
+	num_cubed = num * num * num
+	return num_cubed
+	
+print(cuber())		# uses the default 2
+print(cuber(3))		# 3 overrides the default
+
+# you can pass in multiple values, and return multiple values
+# but order is important
+def solve_triangle(base, height, side1, side2, side3):
+	area = base * height / 2
+	perimeter = side1 + side2 + side3
+	return area, perimeter
+	
+area, perim = solve_triangle(3, 4, 5, 3, 4)	# b=3, h=4, s1=5, s2=3, s3=4
+print('Area:', area, ' Perimeter:', perim)
+
+# above are all called "positional arguments", and order matters
+# you can also pass in "keyword arguments" when calling a function
+a, p = solve_triangle(side1=5, side2=3, side3=4, height=4, base=3)
+print(a, p)
+
+# or use a combination of both, but positional arguments must come first
+a, p = solve_triangle(3, 4, side3=4, side2=3, side1=5)
+print(a, p)
+	
+# CLASSES & OBJECTS
+# ------------------------------------------------
+# Use classes to model real-world things. 
+# Keep related data (variables) and actions (functions) in one block of code.
+class Circle:
+	# Circle constructor -- __init__ method creates a new Circle object
+	def __init__(self, r = 1):
+		self.radius = r
+		
+	def getPerimeter(self):
+		return 2 * self.radius * 3.14
+		
+	def getArea(self):
+		return self.radius ** 2 * 3.14
+# all methods have the self parameter, which is Python's reference to the object that invoked the method
+
+# this calls the __init__ method, which creates the new Circle
+circle1 = Circle(3)		
+# you can access the circle's attributes and methods using the dot operator
+print("Radius =", circle1.radius)
+print("Perimeter =", circle1.getPerimeter())	
+
+# IMPORTS
+# ------------------------------------------------
+# Python has many many classes already written that you can use
+# To access methods and data from another class you must import it
+import math
+print(math.pi)
+
+import random
+print(random.randint(1,5))
+
+# shorter version, using as to abbreviate module name
+import math as m
+print(m.pi)
+
+import random as rd
+print(rd.randint(1,5))
+
+# import just one or two functions or constants rather than a whole module
+# easier for coding, but need to beware names don't conflict
+from math import pi
+print(pi)
+
+from random import randint, shuffle
+print(randint(1,5))
+x = ['a', 'b', 'c']
+shuffle(x)
+print(x)
+
+# can rename an imported function if you want
+x = ['a', 'b', 'c']
+from random import shuffle as sf
+sf(x)
+print(x)
+
+# can also import whole module using *
+from random import *
+print(randint(1,5))
+
+# FILE READ & WRITE
+# ------------------------------------------------
+filename = 'city_data.txt'
+
+# this opens a file handle called fin, iterates the lines of the file, and prints each line
+with open(filename) as fin:
+    for line in fin:
+        print(line)
+
+# we can grab words from a line by using split, which turns each line into a list called row
+with open(filename) as fin:
+    fin.readline()
+    for line in fin:
+        row = line.split(',')
+        print('Country:', row[1], ' City:', row[2])
+
+# use the w parameter to write to an output file
+with open('Cities.txt', 'w') as fout:
+    with open(filename) as fin:
+        fin.readline()
+        for line in fin:
+            row = line.split(',')
+            fout.write(row[2] + '\n')
+
+
+
+
+
+
+
+
+
diff --git a/Python in 90 minutes/test.py b/Python in 90 minutes/test.py
new file mode 100644
index 00000000..7e4f3280
--- /dev/null
+++ b/Python in 90 minutes/test.py	
@@ -0,0 +1,15 @@
+import unittest
+from Python_in_90_minutes import cuber, solve_triangle  # replace with your actual file name (without .py)
+
+class TestBasics(unittest.TestCase):
+    def test_cuber(self):
+        self.assertEqual(cuber(3), 27)
+        self.assertEqual(cuber(), 8)  # default param test
+
+    def test_solve_triangle(self):
+        area, perimeter = solve_triangle(3, 4, 3, 4, 5)
+        self.assertAlmostEqual(area, 6.0)
+        self.assertEqual(perimeter, 12)
+
+if __name__ == '__main__':
+    unittest.main()
\ No newline at end of file