Introduction to Python¶

my_variable = 2
print(my_variable)
type(my_variable)

my_varible = my_variable+1
print (my_variable)

print(3/4)
print(3.0 / 4.0)
print(3%4)
print(3//4)
print(3**4)

a = 3
b = 4
print(a/b)
print(float(a)/float(b))

for i in range(1,10):
     print(i)

i = 1
while i < 10:
    print(i)
    i+=1

a = 20
if a >= 22:
   print("if")
elif a >= 21:
    print("elif")
else:
    print("else")

a = 23
if a >= 22:
   print("if")
    print("greater than or equal 22")
elif a >= 21:
    print("elif")
else:
    print("else")

a = 23
if a >= 22:
   print("if")
   print("greater than or equal 22")
elif a >= 21:
    print("elif")
else:
    print("else")

a = "1"

try:
  b = a + 2
except:
  print(a, " is not a number")

a = "1"
b = a + 2

def Division(a, b):
    print(a/b)
Division(3,4)
Division(3.0,4.0)
Division(3,4.0)
Division(3.0,4)

def Division(a, b):
    print(a/b)
Division(2,"2")

def Division(a, b):
    try:
        print(a/b)
    except:
        if b == 0:
           print("cannot divide by zero")
        else:
           print(float(a)/float(b))
Division(2,"2")
Division(2,0)

a = "A string of characters, with newline \n CAPITALS, etc."
print(a)
b=5.0
newstring = a + "\n We can format strings for printing %.2f"
print(newstring %b)

a = "ABC DEFG"
print(a[1:3])
print(a[0:5])

a = "ABC defg"
print(a.lower())
print(a.upper())
print(a.find('d'))
print(a.replace('de','a'))
print(a)
b = a.replace('def','aaa')
print(b)
b = b.replace('a','c')
print(b)
b.count('c')

import numpy
import numpy as np # using an alias
import numpy.linalg as la # modules can have submodules
from numpy import sin, cos, tan # bring trig functions into global namespace
from numpy import * # frowned upon because it pollutes the namespace

# YOUR CODE HERE

# range(start, stop, step)
# for loop
# print function
# % operator
# check for equality
# if-elif-else control flow

for i in range(1, 101):
    if i % 15 == 0:
        print("FizzBuzz")
    elif i % 3 == 0:
        print("Fizz")
    elif i % 5 == 0:
        print("Buzz")
    else:
        print(i)

x = 3
y = 4
# YOUR CODE HERE

# use of temporary variable
# tuple unpacking

tmp = x
x = y
y = x
print x, y

x = 3
y = 4
x, y = y, x
print x, y

# YOUR CODE HERE

# euclidean distance formula
# operators **
# square root function
# anatomy of a function

u = (3, 0)
v = (0, 4)

((v[0] - u[0])**2 + (v[1] - u[1])**2)**0.5

def euclidean(u, v):
    """Returns the Euclidean distance between points u and v."""
    return ((v[0] - u[0])**2 + (v[1] - u[1])**2)**0.5

euclidean(u, v)

s = """
Write a program that prints the numbers from 1 to 100.
But for multiples of three print 'Fizz' instead of the number and f
or the multiples of five print 'Buzz'. For numbers which are
multiples of both three and five print 'FizzBuzz'
"""

# YOUR CODE HERE

# string methods
# dictionary
# for loop
# collections.Counter

# Version 1
print s.lower().count('a')

# Version 2
counter1 = {}
for _ in s.lower():
    counter1[_] = counter1.get(_, 0) + 1
print counter1['a']

# Version 3
from collections import defaultdict
counter2 = defaultdict(int)
for _ in s.lower():
    counter2[_] += 1
print counter2['a']

# Version 4
from collections import Counter
counter3 = Counter(s.lower())
print counter3['a']

s = """
Write a program that prints the numbers from 1 to 100.
But for multiples of three print 'Fizz' instead of the number and f
or the multiples of five print 'Buzz'. For numbers which are
multiples of both three and five print 'FizzBuzz'
"""

# YOUR CODE HERE

# string constants
# translate method
# replace method
# slicing iterables
# len function

import string
s1 = s.lower().translate(None, string.punctuation).replace(' ', '').replace('\n', '')

count = 0
start = 0
stop = 5

while (stop <= len(s1)):
    # print s1[start:stop]
    if 'a' in s1[start:stop]:
        count += 1
    start += 1
    stop += 1

print count

x = [36, 45, 58, 3, 74, 96, 64, 45, 31, 10, 24, 19, 33, 86, 99, 18, 63, 70, 85,
 85, 63, 47, 56, 42, 70, 84, 88, 55, 20, 54, 8, 56, 51, 79, 81, 57, 37, 91,
 1, 84, 84, 36, 66, 9, 89, 50, 42, 91, 50, 95, 90, 98, 39, 16, 82, 31, 92, 41,
 45, 30, 66, 70, 34, 85, 94, 5, 3, 36, 72, 91, 84, 34, 87, 75, 53, 51, 20, 89, 51, 20]

# YOUR CODE HERE

# sort and remove duplicates
# negative indexing

# version 1
sorted_x = sorted(x)
unique_x = [sx[0]]
for _ in sorted_x[1:]:
    if _ != unique_x[-1]:
        unique_x.append(_)

print unique_x
print len(x)
print len(unique_x)

# using set
print list(set(x))
print len(x)
print len(set(x))

# YOUR CODE HERE

# getting comforatble with functions
# unit tests

def square(x):
    """Returns x^2."""
    return x**2

def cube(x):
    """Returns x^3."""
    return x**3

def pow6(x):
    """Returns x^6."""
    return cube(square(x))

# use of assert for testing
def test_pow6(x):
    assert(abs(pow6(x) - x**6) < 1e-6)

xs = [-2, 0, 1.5]
for x in xs:
    test_pow6(x)

# YOUR CODE HERE

# list comprehensions
# map
# lambda functions

cubes1 = []
for i in range(1, 11):
    cubes1.append(i**3)
print cubes1

cubes2 = [i**3 for i in range(1, 11)]
print cubes2

print map(lambda x: x**3, range(1, 11))

# YOUR CODE HERE

# nested list comprehsnions
# inner and outer loops

print([(i, j) for i in range(1,4) for j in range(10, 14)])
print

pythagorean_triples = [(a, b, c) for a in range(1, 100)
                                 for b in range(1, 100)
                                 for c in range(1, 100)
                                 if a**2 + b**2 == c**2]
print pythagorean_triples
print

pythagorean_triples = [(a, b, c) for a in range(1, 100)
                                 for b in range(a, 100)
                                 for c in range(b, 100)
                                 if a**2 + b**2 == c**2]
print pythagorean_triples

def f(xs):
    """Return normalized list summing to 1."""
    s = 0
    for x in xs:
        s += x
    return [x/s for x in xs]

# YOUR CODE HERE

# elementary debugging

def f(xs):
    """Return normalized list summing to 1."""
    s = 0
    for x in xs:
        s += x
    return [x/s for x in xs]

xs = [1.1,2.2,3.3,4.4]
print f(xs)

xs = [1,2,3,4]
print f(xs)


def f(xs):
    """Return normalized list summing to 1."""
    s = 0.0
    for x in xs:
        s += x
    return [x/s for x in xs]


xs = [1.1,2.2,3.3,4.4]
print f(xs)

xs = [1,2,3,4]
print f(xs)