Tuple

A tuple is an immutable list of values.  Iteration and indexes work the same way as lists, but they cannot be modified.  While list literals use square brackets, tuple literals use parenthesis.

x = (1,4,6)
print(x[0])
1

for val in x:
    print(val)

Assignment

(x,y) = (4,'Fred')
print(y)
Fred

print(x)
4

Iteration

Method items() in dictionary returns a list of tuples.  In a for loop we use as many iteration variables as there are elements in the tuples

for k,v in dictionary.items():
    print(k, v)

for (k,v) in dictionary.items():
    print(k, v)

Comparison Operators

The first element of a tuple is the most significant.  The comparison operator is applied to one element at a time starting with the first element in both tuples

(0,1,2) < (4,6,2)
True

Sorting a list of tuples

# Prints pairs ordered by keys
for k,v in sorted(dictionary.items()):
    print(k,v)

# Sort by values
c = {'a':10 , 'b':1 , 'c':22}
tmp = list()
for k,v in c.items():
    tmp.append((v,k))
print(tmp)
[(10,'a'), (1,'b'), (22,'c')]

tmp = sorted(tmp, reverse=True)
print(tmp)
[(22,'c'), (10,'a'), (1,'b')]