Lsn15_Tuples

8/7/2019 Lsn15_Tuples

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Python Mini-Course

University of Oklahoma

Department of Psychology

Day 4 Lesson 15Tuples

5/02/09Python Mini-Course: Day 4 Lesson 151


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Lesson objectives

1. Describe the characteristics of thetuple data structure in Python

2. Perform basic operations with tuplesincluding creation, conversion,repetition, slicing, and traversing

3. Use tuples in functions4. Use tuples to traverse multiple

sequences simultaneously



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The tuple data structure

yIn Python, a tuple is animmutable sequence of valuesyEach value in the tuple is anelementor item

yElements can be any Python data

typeyTuples can mix data types

yElements can be nested tuples



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Creating tuples

numbers = (1, 2, 3, 4)

print numbers

cheeses = ('swiss', 'cheddar','ricotta', 'gouda')

print cheeses



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Creating tuples

t1 = ('a')

print t1, type(t1)

t2 = ('a',)print t2, type(t2)

t3 = tuple('a')

print t3, type(t3)

empty = tuple()

print empty



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Creating tuples

alist = [1, 2, 3, 4]

atuple = tuple(alist)

print atuplestr = 'parrot'

atuple = tuple(str)

print atuple



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Tuple indexing

yJust like other sequences,elements within a tuple are

indexedprint cheeses[0]

yTuples are immutable

cheeses[0] = 'Feta'



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Slicing a tuple

yLike other sequences, tuples canbe sliced

print cheeses[1:4]

*Slicing a tuple creates a new tuple. Itdoes not change the original tuple.



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Using the + operator

a = (1, 2, 3)

b = (4, 5, 6)

c = a + b

print a, b, c

*The + operator returns a new tuple

that is a concatenation of two tuples



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Operations on tuples

y Tuples support all the standardsequence operations, including:y

Membership tests (using the in keyword)yComparison (element-wise)

y Iteration (e.g., in a for loop)

yConcatenation and repetition

yThe len function



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Tuples and functions

yMany Python functions returntuples

yRemember that a function canonly return one valueyHowever, if multiple objects are

packaged together into a tuple, thenthe function can return the objectsinside a single tuple



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Passing tuples as arguments

yA parameter name that beginswith * gathers all the arguments

into a tupleyThis allows functions to take avariable number of arguments



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Example

def printall(*args):

print args

printall(1, 2.0, 'three')



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Example: pointless.py

def pointless(required, optional=0, *args):

print 'Required: %s' % required

print 'Optional: %s' % optional

if args: print 'Others: %s' % str(args)print

pointless(1)

pointless(1, 2)

pointless(1, 2.0, 'three')

pointless(1, 2.0, 'three', [4])



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The zip function

yBuilt-in function that takes two ormore sequences and zips them

into a list of tuples, where eachtuple contains one element fromeach sequence



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The zip function

yExample:s = 'abc'

t = [0, 1, 2]

z = zip(s, t)

print z



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The zip function

yIf the sequences are not thesame length, the result has the

length of the shorter one

print zip('Anne', 'Elk')



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Using tuple assignment in a for loop

t = [('a', 0), ('b', 1), ('c', 2)]

for letter, number in t:

print number, letter



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Synchronized traversing: has_match.py

def has_match(t1, t2):

for x, y in zip(t1, t2):

if x == y:

return True

return False

a = [5, 4, 9, 7, 10]

b = [4, 3, 5, 7, 15]

print has_match(a, b)


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