Useful Python CMSC 120: Visualizing Information. Scope def area(diameter): radius = diameter / 2.0 A…

Useful Python

CMSC 120: Visualizing Information

Scopedef 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()

Global VariablesPI = 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()

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()

Our Histogram Problem

Histogram

(0,0)

(offset, offset)

Which parts of the program need to access:the window?the offset?

Our Histogram Problem

Histogram

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TicksLabelsTitle

Doing MathPylabmath library

an application programming interface or APIset of useful functions

>>> from math import *>>> pi3.1415926535897931

functions/constants defined in an API turn purple

math APIpow(x, y)

returns x**y.

sqrt(x) returns the square root of x

math APIceil(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.

math APImin(x)

returns minimum value in list x

max(x)returns maximum value in list x

sum(x)returns sum of values in list x

math APITrigonometric functions

sincosasinacostanatandegreesRadians

Logarithm functionsTwo Constants: pi, e

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

Using the math APIfrom 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

Using the math API

from math import *

def calcBinSize(data, numBins): rng = max(data) – min(data) return ceil(rng / float(numBins))

Significant DigitsDigits in a number that are meaningful

Depend on number of significant digits in data

Significant Digits in CalculationsThe 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.

Why Care?

>>> 22/3.56.2857142857142856

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

Outputting Numbers>>> print 'The value of pi is ' , pi3.1415926535897931

Value of pi, 3 places after the decimal point:

>>> print 'The value of pi is %5.3f' % pi3.142

Formatting

'The value of pi is %5.3f' % pi

<string> % <expression>

<string>: contains a format specification for the value to be inserted at that pointBegins with % - signEnds with f: floating point valueNumber between % and f specifies the format

Formatting

'The value of pi is %5.3f' % (pi)

<string> % <expression>

<expression>: contains the value to be formatted

Numerical Specificationsf: floatd: integers: string

>>> print 'My choice was %10s' % 'Rock'My choice was Rock

Justification: -, +

>>> print 'My choice was %-10s' % 'Rock'My choice was Rock