CS61A Lecture 12: Lists & Dictionaries

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Computer Science
De Nero

For Statements stairs = (1, 2, 3, 4, 5, 4, 3, 4, 5, 6, 7) from operator import getitem def count_while(s, value, getitem=getitem, len=len): """Count the number of occurrences of value in sequence s. >>> stairs.count(4) 3 >>> count_while(stairs, 4) 3 """ total, index = 0, 0 while index < len(s): if getitem(s, index) == value: total = total + 1 index = index + 1 return total def count(s, value): """Count the number of occurrences of value in sequence s. >>> count(stairs, 4) 3 """ total = 0 for elem in s: if elem == value: total = total + 1 return total For simpler than using While Loop Sequence Iteration Using For Statements Name after for bound in the first frame of current environment (not new frame) Execution Procedure: for in : 1. Evaluate header , which yield iterable value (sequence) 2. For each element in sequence, in that order: 1. Bind to that element in first frame of current environment 2. Execute Sequence Unpacking in For Statements A sequence of fixed-length sequences (i.e. pairs) A name for each element in a fixed-length sequence Each name bound to value, multiple assignment Ranges A sequence of consecutive integers Length: ending value - starting value Element selection: starting value + index Ex: range(-2 , 2) is from -2 to 1, not include 2 range(4) is from 0 to 4, assume 0 starting value Can use tuple constructor for ranges Membership & Slicing Membership: 2 in (2, 3): True The in word checks whether the name is found inside the list Slicing: [0:2] creates new objects by splitt
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