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Lab #5-6 Follow-Up: More Python ; Images

Lab #5-6 Follow-Up: More Python ; Images. Part 1: Python Conditionals, Return Values, and Lists. Conditionals: General Form . if <CONDITION> : <statement> <statement> ... <statement> elif <CONDITION> : <statement> ... <statement> elif ... else: <statement>

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Lab #5-6 Follow-Up: More Python ; Images

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  1. Lab #5-6 Follow-Up:More Python; Images

  2. Part 1: Python Conditionals, Return Values, and Lists

  3. Conditionals: General Form if <CONDITION> : <statement> <statement> ... <statement> elif <CONDITION> : <statement> ... <statement> elif ... else: <statement> ... <statement>

  4. Example if IQ > 140: print("OMG genius!") elif IQ > 130: print("Wicked smaht!") elif IQ > 120: print("Way above average.") elif IQ > 110: print("Still no slouch.") elif IQ > 100: print("College material.") elif IQ > 90: print("Hope springs eternal!") else: print("Dude, where's my car?")

  5. Comparison Operators x > y # x greater than y x < y # x less than y x >= y # x greater than or equal to y x <= y # x less than or equal to y x != y # x not equal to y

  6. Logical / Boolean Operators x > y and y > z x > y or y > z not (x > y) G. Boole (1815-1864)

  7. Logic Gates: The Building Blocks of Digital Circuits http://volga.eng.yale.edu/uploads/Main/gate-symbols.png

  8. Logic Gates: The Building Blocks of Digital Circuits http://cpuville.com/logic_gates.htm http://volga.eng.yale.edu/uploads/Main/gate-symbols.png resistor transistor

  9. Putting It All Together # The grading scale will be 93-100 A; 90-92 A-; 87-89 B+; # 83-86 B; 80-82 B-; 77-79 C+; 73-76 C; 70-72 C-; # 67-69 D+; 63-66 D; 60-62 D-; below 60 F. if average >= 93 and average <= 100: grade = 'A' elif average >= 90 and average <= 92: grade = 'A-' elif average >= 87 and average <= 89: grade = 'B+' elif average >= 83 and average <= 86: grade = 'B' elif average >= 80 and average <= 82: grade = 'B-' . . . elif average < 60: grade = 'F'

  10. Less Is More! # The grading scale will be 93-100 A; 90-92 A-; 87-89 B+; # 83-86 B; 80-82 B-; 77-79 C+; 73-76 C; 70-72 C-; # 67-69 D+; 63-66 D; 60-62 D-; below 60 F. if average >= 93: grade = 'A' elif average >= 90: grade = 'A-' elif average >= 87: grade = 'B+' elif average >= 83: grade = 'B' elif average >= 80: grade = 'B-' . . . else: grade = 'F'

  11. if average >= 93: grade = 'A' elif average >= 90: grade = 'A-' elif average >= 87: grade = 'B+' elif average >= 83: grade = 'B' elif average >= 80: grade = 'B-' . . . else: grade = 'F' Dimes Pennies Nickels Quarters

  12. Returning Values from Functions • For many robot applications, functions just need to cause side-effects: def wiggle(speed, waitTime): rotate(-speed) wait(waitTime) rotate(speed) wait(waitTime) stop() • Outside of robotics, functions are described by what value they return as well ….

  13. Returning Values from Functions def square(x): return x * x # without square(), we'd have to do this: dst = sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2)) # instead of this: dst = sqrt(square(x1-x2) + square(y1-y2))

  14. Multiple return points def absoluteValue(x): if x < 0: return –x elif x > 0: return x elif x == 0: return 0

  15. Less is more! def absoluteValue(x): if x < 0: return –x else: return x

  16. Putting it all together: Writing our own sqrt()function • For perfect squares (0, 1, 4, 9, 16, 25, …) , we typically just memorize them • For other numbers, we need a function: • from math import sqrt • How does sqrt() work? E.g., what is sqrt(3) ?

  17. Putting it all together: Writing our own sqrt()function • How does sqrt() work? E.g., what is sqrt(3) ? • It must be between 0 and 3, since a square root can't be negative, and a number can't be bigger than its own square root (?) • So our first approximate could just be the average of 0 and 3: (0 + 3) / 2 = 1.5 • But 1.5 * 1.5 = 2.25, which is less than 3 • So the square root must lie between 1.5 and 3 • (1.5 + 3) / 2 = 2.25; 2.25 * 2.25 = 5.0625, too big! • So the square root must lie between 1.5 and 2.25 • Et cetera

  18. Putting it all together: Writing our own sqrt()function • Algorithm for computing the square root of a number N: • Start with a lower bound of zero and an upper bound equal to N • While the square of their mean is too far from N, do the following: • If squared mean is too big, use mean as the new upper bound • Otherwise, use mean as new lower bound • What haven't we considered?

  19. PRECISION = 0.000001 def mysqrt(n): if n < 1: lower = n upper = 1 else: lower = 1 upper = n while True: mean = (lower + upper) / 2.0 meansqr = mean * mean if abs(meansqr-n) < PRECISION: return mean if meansqr > n: upper = mean else: lower = mean

  20. Python Lists • Computer Science consists mainly in • Putting data into lists • Sorting the lists according to some criterion (e.g. alphabetical order) • Searching the sorted list to find an item of interest • For sorting and searching to be efficient, the lists must support random access : like RAM (vs. sequential access of disk, one byte at a time) • Python lists provide all these features for us • Python's range() function generates numerical lists of arbitrary size

  21. Self-Test: Predict the result of each print() family = ['Simon', 'Linda', 'Sam'] print(family[0]) # random access print(family[1]) print('Simon' in family) # search print('George' in family) cousins = ['Stephanie', 'Susan', 'Michael'] print(family + cousins) family.sort() print(family) print(len(family)) family.append('Sharon') print(family) family.reverse() print(family) for person in family: print(person)

  22. Self-Test: Predict the result of each print() for k in range(5): print(k) for k in range(3,7): print(k) for k in range(1,10,2): print(k)

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