1. Useful Python CMSC 120: Visualizing Information

2. Scope def area(diameter): radius = diameter / 2.0 A = PI * radius ** 2 return A def circumference(diameter): return PI * diameter def main(): PI = 3.14 d = input('Enter a diameter:') print area(d), circumference(d) main()

3. Global Variables PI = 3.14 def area(diameter): radius = diameter / 2.0 A = PI * radius ** 2 return A def circumference(diameter): return PI * diameter def main(): d = input('Enter a diameter:') print area(d), circumference(d) main()

4. Parameters def area(diameter, P): radius = diameter / 2.0 A = P * radius ** 2 return A def circumference(diameter, P): return P * diameter def main(): d = input('Enter a diameter:') print area(d, P), circumference(d, P) main()

5. Our Histogram Problem Histogram (0,0) (offset, offset) Which parts of the program need to access: the window? the offset? Which parts of the program need to access: the window? the offset?

6. Our Histogram Problem Histogram (0,0) Ticks Labels Title Ticks Labels Title

7. Doing Math Pylab math library an application programming interface or API set of useful functions >>> from math import * >>> pi 3.1415926535897931 functions/constants defined in an API turn purple

8. math API pow(x, y) returns x**y. sqrt(x) returns the square root of x

9. math API ceil(x) returns the ceiling of x as a float, the smallest integer value greater than or equal to x. floor(x) returns the floor of x as a float, the largest integer value less than or equal to x.

10. math API min(x) returns minimum value in list x max(x) returns maximum value in list x sum(x) returns sum of values in list x

11. math API Trigonometric functions sin cos asin acos tan atan degrees Radians Logarithm functions Two Constants: pi, e

12. Using the math API def calcBinSize(data, numBins): data.sort() mn = data[0] mx = data[len(data) - 1] return (mx - mn) / float(numBins) >>> d = range(20, 40, 2) >>> calcBinSize(d, 4) 4.5

13. Using the math API from math import * def calcBinSize(data, numBins): data.sort() mn = data[0] mx = data[len(data) - 1] return ceil((mx - mn) / float(numBins)) >>> d = range(20, 40, 2) >>> calcBinSize(d, 4) 5.0

14. Using the math API from math import * def calcBinSize(data, numBins): rng = max(data) – min(data) return ceil(rng / float(numBins))

15. Significant Digits Digits in a number that are meaningful Depend on number of significant digits in data Significant Digits in Calculations The number of significant digits in an answer should equal the least number of significant digits being multiplied or divided The number of decimal places in the answer should be the same as the least number of decimal places in any of the numbers being added or subtracted.

16. Why Care? >>> 22/3.5 6.2857142857142856 Computers have ability to calculate to a high degree of precision But...they are producing more information than input All those extra digits take up space

17. Outputting Numbers >>> print 'The value of pi is ', pi 3.1415926535897931 Value of pi, 3 places after the decimal point: >>> print 'The value of pi is %5.3f' % pi 3.142

18. Formatting 'The value of pi is %5.3f' % pi % : contains a format specification for the value to be inserted at that point Begins with % - sign Ends with f: floating point value Number between % and f specifies the format

19. Formatting 'The value of pi is %5.3f' % (pi) % : contains the value to be formatted

20. Numerical Specifications f: float d: integer s: string >>> print 'My choice was %10s' % 'Rock' My choice was Rock Justification: -, + >>> print 'My choice was %-10s' % 'Rock' My choice was Rock