P3 Python - TYL - Tuples and Sets.

1. Write a Python program to replace last value of tuples in a list.  
Sample list: [(10, 20, 40), (40, 50, 60), (70, 80, 90)]
Expected Output: [(10, 20, 100), (40, 50, 100), (70, 80, 100)]

Remember that tuples are immutable.
A singleton tuple can be created only by following a value by a comma.
To change an item in a tuple, you can slice and then concatenate the value required, create a new tuple
For this program,
 lst_tup[i]=lst_tup[i][:2]+(100,) is equivalent to   lst_tup[i]=lst_tup[i][:-1]+(100,)
If we want to generalize to remove last element of any length of the tuple the later should be used.

Program:

lst_tup= [(10, 20, 40), (40, 50, 60), (70, 80, 90)]

for i in range(0, len(lst_tup) ):
    #slices the first two elements, appends 100 to the end in another tuple.
     lst_tup[i]=lst_tup[i][:-1]+(100,)

print(lst_tup)

Output:

[(10, 20, 100), (40, 50, 100), (70, 80, 100)]

Using List comprehension:

lst_tup= [(10, 20, 40), (40, 50, 60), (70, 80, 90)]
lst_tup=[x[:-1]+(100,) for x in lst_tup]
print(lst_tup)

2. Write a Python program to sort a tuple by its float element. 

Sample data: [('item1', '12.20'), ('item2', '15.10'), ('item3', '24.5')]
Expected Output: [('item3', '24.5'), ('item2', '15.10'), ('item1', '12.20')]

Method 1 :
lst_tuple=[('item1', '12.20'), ('item2', '15.10'), ('item3', '24.5')]

#use DSU
#bring the key you want to the front
lst = []
for key,val in lst_tuple: #decorate
    lst.append( (val,key) )

lst.sort() #sort
sorted_lst=[]
for val,key in lst: #undecorate
    sorted_lst.append( (key,val) )
 
print(sorted_lst)
Output:
[('item1', '12.20'), ('item2', '15.10'), ('item3', '24.5')]

Method 2 :
Use the sort() method
list.sort(reverse=True|False, key=myFunc)

You can specify a different key by passing a function to it that returns the key.  In our case we want the second element.

def myFunc(e):
    return e[1]

lst_tuple=[('item1', '12.20'), ('item2', '15.10'), ('item3', '24.5')]
lst_tuple.sort(key=myFunc)

Method 3:
This can be written more briefly by using a lambda function which is an anonymous function in Python

lst_tuple=[('item2', '15.10'),('item1', '12.20'),('item3', '24.5')]
lst_tuple.sort(key=lambda e:e[1])
print("Using lambda:", lst_tuple)


3. Use python set to check if string is panagram, i.e., a sentence that uses every letter in the alphabet.

-Generates lowercase alphabets from a to z using inbuilt functions or manually,
- convert the string to check for panagram to lower case
- convert it into a set
- the string might contain other special characters or whitespaces.
- so set of alphabets should be a subset of the set of characters in the string.

Program:
alp=''
for asc in range(ord('a'), ord('z')+1):
    alp+=chr(asc)

def panagram(s):
    s= s.lower()
    if set(alp).issubset(set(s)):
        print("Panagram")
    else: print("Not a Panagram")

s='The quick brown fox jumps over the lazy dog!'
print(s)
panagram(s)
s='The quick brown fox jumps over the fence.'
print(s)
panagram(s)

Output:

The quick brown fox jumps over the lazy dog!

Panagram

The quick brown fox jumps over the fence.

Not a Panagram

4. Use python sets to check if two lists have at-least one element in common

Convert both the lists to sets
find intersection.
Either check if length of the intersection set is at least 1 OR
check if the resulting set after intersection is not an empty set, set()

Program:

def checkcommon(a,b):
    inter = set(a) & set(b)
    #print('Debug',inter)
    if inter != set():
        print('Has at least one common element')
    else : print('Does not have a common element')


lst1 = [2,5,6,7,8]
lst2 = [10,2,5,6,8]
lst3 = [11,12,13]
print(lst1,lst2)
checkcommon(lst1,lst2)

print(lst1,lst3)
checkcommon(lst1,lst3)


Alternative:
def checkcommon(a,b):
    inter = set(a) & set(b)
    #print('Debug',inter)
    if len(inter) >=1:
        print('Has at least one common element')
    else : print('Does not have a common element')

Output:

tyl_list_common.py
[2, 5, 6, 7, 8] [10, 2, 5, 6, 8]
Has at least one common element
[2, 5, 6, 7, 8] [11, 12, 13]
Does not have a common element

5. Write a Python program to find maximum and the minimum value in a set

Program:

s= {10,2,5,6,8}
max_val =max(s)
min_val = min(s)
print('Maximum value',max_val)
print('Minimum value', min_val)

Output:

Maximum value 10
Minimum value 2