COMP10001 Lecture Notes - Lecture 8: Iter, Iterator, Plaintext
25 May 2018
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CSV = comma
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separated values
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Stores tabulated data as plain
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text, separated by commas
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import csv
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use csv.DictReader() to import the data into a list of dictionaries
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use csv.reader() to import the data into a list of lists
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CSV files:
iterator = object that keeps track of the traversal of a container
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an iterable object will return an iterator object when passed to the built
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in Python function
iter()
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__next__ method returns the next thing in the iteration and updates their state/memory of
where they are up to
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StopIteration exceptions is raised when the container is empty
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iterators are more memory efficient than storing and indexing a whole iterable
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no random access
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"remembers" last item seen
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no len()
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can be infinite
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traverse exactly once (forwards)
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characteristics:
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Iterators:
implements a number of iterator "building blocks"
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standardises a set of fast, memory efficient tools
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forms an "iterator algebra"
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product = cross
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product of sequences
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cycle = repeat items indefinitely
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groupby = group items by some criterion
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combinations = n choose k
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useful functions
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The itertools module:
break the problem down into smaller sub
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problems
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solve each sub
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problem the same way as the big problem
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recursive function definitions are often used to solve problems in a divide
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and
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conquer
manner
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recursive function calls on smaller inputs
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a reachable base case to ensure the calculation halts
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generally made up of two parts
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head recursion = recurse first, then perform some local calculation
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tail recursion = perform some local calculation, then recurse
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Recursion:
Week 8
Thursday, 3 May 2018 11:34 AM
Foundations of Computing Page 1
