Write following python script with your text editor.

Then, run ‘python your_script.py’

If you got ‘Hello World’, go on to the next slide.

def main():

print ‘Hello World’

if __name__ == ‘__main__’:

main()

Lists – compound data type l = [1,2,3,5] # defines a list contains 1, 2, 3, 5

print l[0] # getting a value

l[0] = 6 # setting a value

l.append(7) # adding to list

print l # will print ‘[6, 2, 3, 5, 7]’

l.extend([8, 9, 10]) # connecting another list

print l # will print ‘[6, 2, 3, 5, 7, 8, 9, 10]’

print range(3) # stops at 2

print range(1, 3) # starts at 1 and stops at 2

print range(0, 5, 2) # start: 1 stop: 4 and steps by 2

Create following lists with range function.

1. [0, 1, 2, 3, 4]

2. [3, 4, 5, 6, 7]

3. [3, 6, 9, 12, 15, 18]

4. [2, 4, 6, 8, 12, 16, 20] hint: use + operator

Answer:

1. range(5)

2. range(3, 8)

3. range(3, 21, 3)

4. range(2, 10, 2) + range(12, 24, 4)

Dictionaries – compound data type

Found in other languages as “map”, “associative memories”, or “associative arrays”

Lists vs Dictionaries › You can use only integer number as index on lists

Like a[0], a[-1]

› You can use integer numbers and strings as key on dictionaries(if its value exists)

Like d[0], d[‘foo’], d[‘bar’]

Creating a dictionary tel = {‘John’:8000, ‘Jane’:8001, ‘Joe’:8002}

Adding key and value tel[‘Joan’] = 8003 Getting value from key tel[‘Jane’]

Setting value from key tel[‘Joe’] = 0004 Removing value from key del tel[‘John’] Getting key list of a dictionary

tel.keys()

Crate a dictionary from two lists

names = [‘John’, ‘Jane’, ‘Joe’]

tel = [8000, 8001, 8002]

tel = dict(zip(names, tel))

Create a dictionary that

› Keys are [0, 1, …, 10]

› Values are (key) * 2

› i.e. d[0]=0, d[1]=2, d[2]=4, …, d[10]=20

Answer:

k = range(11)

v = range(0, 11*2, 2)

d = dict(zip(k, v))

Logical Operator

if statements

for statements

Compares two values print 1 < 2 print 1 > 2

print 1 == 2

print 1 <= 2

print 1 >= 2

And, Or, and Not print 1 < 2 and 1 == 2

print 1 < 2 or 1 > 2

print not 1 == 2

x = int(raw_input(‘value of x: ’))

if x < 0:

print(‘x is negative’) # must indent

elif x > 0:

print(‘x is positive’)

else:

print(‘x is not positive neither negative’)

print(‘i.e. x is zero’)

For integer variable named ‘x’,

› Print ‘fizz’ if x can be divided by 3

› Print ‘buzz’ if x can be divided by 5

(e.g. if x is 10, print ‘buzz’, x is 15, print ‘fizz buzz’)

(hint: use % operator(e.g. 10 % 3 = 1, 14 % 5 = 4))

x = int(raw_input('x value:'))

if x % 3 == 0:

print 'fizz'

if x % 5 == 0:

print 'buzz'

n = int(raw_input(‘list length: ’))

l = []

for i in range(n): # for each number in (0…n-1)

l.append(raw_input(‘%dth word: ’ % i))

for w in l: # for each word in your list

print w

Create a list only contains

› Multiple of 3 or 5 (3, 5, 6, 9…)

› Between 1 and 20

i.e. [3, 5, 6, 9, 10, 12, 15, 18, 20]

l = []

for i in range(1, 21):

if i % 3 == 0 or i % 5 == 0:

l.append(i)

print l

Defining a function

def add(a, b):

return a + b

Calling the function

print add(10, 2)

Recursive call

def factorial(n):

if n <= 0:

return 1

else:

return n * factorial(n-1)

Find the 10-th Fibonacci sequence

› Fibonacci sequence is

0, 1, 1, 2, 3, 5, 8, …

The next number is found by adding up the two

numbers before it(e.g. 5th number 3 = 2 + 1).

def fib(n):

if n <= 1: return 0

elif n == 2:

return 1 else:

return fib(n-1) + fib(n-2)

print fib(10)