Lecture5 List and Dictionary comprehensions

Take home Question

• List of urls is given. Some urls are from same domain, some are from different. Find unique domain names used in the urls.

  urls = ['www.abrakadabra.com/dccEcB/EGdd',
  'www.abrakadabra.com/gADFeD/bcAF',
  'www.abra.com/AGadbb/eagE',
  'www.dabra.com/cffdfD/FCAD',
  'www.abra.com/GFGaBE/dcfc',
  'www.abra.com/gaFegG/Bdaf',
  'www.abrakadabra.com/aGabaf/EEfa',
  'www.dabra.com/ceEgFD/bGgc',
  'www.dabra.com/bDEffC/bcEA']

• Write a function min2 which find minimum from given two numbers. Also write a function min3 which can find minimum number from given 3 numbers. Do not make use of bulit in min function.

Problem 1

1. Find the domain name from url

   url = 'www.abrakadabra.com/dccEcB/EGdd'

2. Then make use of unique function that we wrote in last lecture def unique(items): unique_items = [] for item in items:

    if item not in unique_items:
        unique_items.append(item)
   

   return unique_items

def unique(items):
    unique_items = []
    for item in items:
        if item not in unique_items:
            unique_items.append(item)
    return unique_items

def find_filename(path):
    return path.split("/")[-1]

def find_domain(url):
    return url.split("/")[0]

url = 'www.abrakadabra.com/dccEcB/EGdd'

find_domain(url)

'www.abrakadabra.com'

urls = urls = ['www.abrakadabra.com/dccEcB/EGdd',
'www.abrakadabra.com/gADFeD/bcAF',
'www.abra.com/AGadbb/eagE',
'www.dabra.com/cffdfD/FCAD',
'www.abra.com/GFGaBE/dcfc',
'www.abra.com/gaFegG/Bdaf',
'www.abrakadabra.com/aGabaf/EEfa',
'www.dabra.com/ceEgFD/bGgc',
'www.dabra.com/bDEffC/bcEA']

def unique_domains(urls):
    domains = []
    for url in urls:
        domain = find_domain(url)
        domains.append(domain)
    
    return unique(domains)

unique_domains(urls)

['www.abrakadabra.com', 'www.abra.com', 'www.dabra.com']

def min2(x, y):
    if x < y:
        return x
    else:
        return y

min2(4 , 7)

4

def min3(x, y, z):
    if x < y and x < z:
        return x
    elif y < x and y < z:
        return y
    else:
        return z
    
def min3(x, y, z):
    m = min2(x,y)
    return min2(m,z)

Question find prime numbers less than 100

def primes(n):
    prime_numbers = []
    for i in range(1, n+1):
        primeflag = True
        for j in range(2, i):
            if i%j==0:
                primeflag = False
        if primeflag:
            prime_numbers.append(i)
    
    return prime_numbers

primes(50)

[1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

Some rules for good python programming

1. Give very sensible names to variables and function
2. Decompose your problem well
3. To do , try to explaon your problem in plain english to a non programmer.
4. write small function and compose them together

def filterodd(nums):
    odds = []
    for n in nums:
        if n % 2 == 1:
            odds.append(n)
    return odds

def filter_prime(nums):
    primes = []
    for n in nums:
        if isprime(n):
            primes.append(n)
    return primes


def isprime(n):
    flag = True
    for i in range(2, n):
        if n%i==0:
            flag = False
    return flag

filter_prime(range(1,21))

[1, 2, 3, 5, 7, 11, 13, 17, 19]

def filter_prime(nums):
    primes = []
    for n in nums:
        if isprime(n):
            primes.append(n)
    return primes


def isprime(n):
    flag = True
    for i in range(2, n):
        if n%i==0:
            flag = False
    return flag

def genrate_primes(n):
    """returns prime numbers less than n
    """
    return filter_prime(range(1, n))

genrate_primes(50)

[1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

list slicing

p = genrate_primes(50)

p

[1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

p[0]

1

p[-1]

47

p[-2]

43

p[-5]

31

p[3:7] # items from 3rd index till 7th (exluding)

[5, 7, 11, 13]

p[1:10:2] # every alternater item starting from index 1 till 10 (excluding)

[2, 5, 11, 17, 23]

p[1:10]

[2, 3, 5, 7, 11, 13, 17, 19, 23]

items[start:end:step]

p[3:9] # step is not given so it is taken as 1 by default

[5, 7, 11, 13, 17, 19]

p[:5] # take first 5 items

[1, 2, 3, 5, 7]

p[5:] # drop first 5 items

[11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

p

[1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

p[:] # copy id list

[1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

p[::2]

[1, 3, 7, 13, 19, 29, 37, 43]

p[::-1]  # reverse list

[47, 43, 41, 37, 31, 29, 23, 19, 17, 13, 11, 7, 5, 3, 2, 1]

Question

• Write a function to check if given string is palindrom

def is_palindrom(name):
    return name == name[::-1]

is_palindrom("hello")

False

is_palindrom("mom")

True

is_palindrom(121)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-52-6eb2d0dc3f14> in <module>
----> 1 is_palindrom(121)

<ipython-input-49-af122c970411> in is_palindrom(name)
      1 def is_palindrom(name):
----> 2     return name == name[::-1]

TypeError: 'int' object is not subscriptable

def is_palindrom_number(n):
    return is_palindrom(str(n))

is_palindrom_number(121)

True

is_palindrom_number(123)

False