Python Part4: For loop, argument passing and Tuple

For loop

• items = [a, b, c, d] 
• for item in items: 
•  print(item) 
•  for i in range(5) 
•  print(i)

Argument passing

• Function with arguments.
• def modify(k) 
•  k.append(13) 
•  print(k) 
• m = [6, 7, 8, 9] 
• modify(m) 
• Default arguments.
• def DisplayMessage(m='nothing') 
• print(m) 
• message = 'Welcome to python' 
• DisplayMessage(Message) 
• DisplayMessage()

Tuple

• Heterogeneous immutable collection. 
• Delimited by parentheses.
• For example t = ("norway", 4.953, 3) 
• Items separated by commas.
• Element access with square brackets and zero-based index. T[index] 
• >>> t[0] 
• 'Norway'
• len(t) for number of elements. 
• >>> len(t) 
• 3
• Iteration with for loop. 
• for item in t: 
• print(item) 
• Norway 
• 4.953 
• 3 
• Concatenation with + operator. 
• t + (338186.0, 2659) 
• ('Norway', 4.953, 3, 338186.0, 2659) 
• Reputation with * operator. 
• t * 3 
• ('Norway', 4.953, 3, 'Norway', 4.953, 3, 'Norway', 4.953, 3)
• Tuple can contain any kind of object. 
• Nested tuples.
• A = ((245, 446), (90, 456)) 
• Chain square-brackets indexing to access inner elements. 
• A[1][0] 
• 90 
• Can’t use one object in parentheses as a single element tuple. 
• For a single element tuple include a trailing comma. 
• K = (234, ) 
• The empty tuple is simply empty parentheses. 
• E = ()
• Delimiting parentheses are optional for one or more elements.
• p = 1, 1, 1, 4, 6, 19 
• >>> p 
• (1, 1, 1, 4, 6, 19) 
• Tuples are useful for multiple return values. 
• def MinMax(items) 
• Return Min(items), Max(items) 
• >>> MinMax([33, 30, 9, 82, 87]) 
• (9, 87)
• Tuple unpacking allow us to destructure directly into named references. 
• lower, upper = MinMax([33, 30, 9, 82, 87]) 
• >>> lower 
• 9 
• >>> upper 
• 87
• Tuple unpacking works with arbitrarily nested tuples (although not with other data structure) 
• (a, (b, (c, d))) = (4, (3, (2, 1))) 
• >>> a 
• 4 
• >>> b 
• 3 
• >>> c 
• 2 
• >>> d
•  1 
• a, b = b, a is the idiomatic python swap.
• Use the tuple constructor to create tuples from other iterable series of objects. 
• >>> tuple([234, 444, 897]) 
• (234, 444, 897) 
• >>> tuple("car") 
• ('c', 'a', 'r') 
• The in and not in operators can be used with tuples - and other collection types – for membership testing. 
• >>> 5 in (3, 5, 9, 13) 
• True 
• >>> 5 not in (3, 5, 9, 13) 
• False

See Also