By ben blake andrew dzambo paul flanagan
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By: Ben Blake, Andrew Dzambo , Paul Flanagan. Python. Spacing Comments Header Consistency with variables – keep it simple Set all variables equal to zero initially Notes on changes to code – version control

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By ben blake andrew dzambo paul flanagan

By: Ben Blake, Andrew Dzambo, Paul Flanagan

Python


General programming tips

  • Spacing

  • Comments

  • Header

  • Consistency with variables – keep it simple

  • Set all variables equal to zero initially

  • Notes on changes to code – version control

  • Good formatting example: http://www.personal.psu.edu/amd5554/resources/documented_code.pdf

General Programming Tips


Python basics

  • Declaring variables – don't need to create variable initially

  • Indenting in loops – no end statement

  • Capitalization matters – Temp, temp, tEmp, TEMP are all different variables

Python Basics


Numerical arithmetic

  • Mathematical expressions are the same

    • + Addition

    • - Subtraction

    • * Multiplication

    • / Division

    • ** Exponentiation

    • 9.8E-8 = 9.8 * (10 ** (-8))

Numerical Arithmetic


Math functions

  • Built-in functions

    • float, int, max, min, abs

  • Imported functions

    • sin, cos, tan, asin, acos, atan, log (natural log), log10 (base 10 log), exp, sqrt, pi, e

  • Trigonometric functions work exclusively in radians

    • k = m.cos(a * m.pi / 180.0)

    • degrad = m.pi / 180.0

    • k = m.cos(a * degrad)

Math Functions


Importing

  • Some commands/functions need to be imported in order to be used

  • Some libraries that can be imported: math, numpy, pylab

  • Different ways to import

    • from math import cos, sin, acos, pi

    • import math

      • k = math.cos(a * m.pi / 180.0)

    • import math as m

      • k = m.cos(a * m.pi / 180.0)

Importing


Shortcut operators

  • Linecount += 1 ==>linecount= linecount + 1

  • Average /= linecount==> average = average / linecount

  • Balance -= payment ==> balance = balance – payment

  • Population *= growth ==> population = population * growth

Shortcut Operators


Input output

  • Need to distinguish between read-only (input) files and writeable (output) files

  • “r” = read-only, “w” = writeable

  • infile = open(“weather.csv”, “r”)

  • outfile = open(“pressure.txt”, “w”)

Input/Output


Using input output files

  • Reading input files

    • vap_list = infile.readlines()

    • for vaporpressure in vap_list:

  • Print statements

    • Print >> outfile, x, y, vaporpressure

    • If a number immediately follows the %, it is the width (in spaces) of the field in which the object will be written

      • Print ‘%4f’ % x, ‘%4f’ % y  this will print x and y as floating point numbers over 4 spaces

Using Input/Output Files


Loops

  • Types: for, if, while loops

  • Indenting denotes code is in loop

  • To close loop, unindent the next line

  • Example of a simple loop - counts # of x's in xlist

    for x in xlist:

    y += 1

    print y

Loops


For loops

  • Determinant loop – use when you know how long you want the program to run

  • Similar to the “do loop” in ForTran and C++

  • Two examples of for loops – can use either an input file or an array

    for station in stations:

    for k in range(n):

For Loops


If loops

  • Used to make logical decisions

  • Can be imbedded inside for loops

    if logical_expression_1:

    # do this block when logical_expression_1 is true

    elif logical_expression_2:

    # do this block when logical_expression_2 is true

    else:

    # do this block when neither logical expression above is true

If Loops


Logical expressions in python

  • Comparisons of one variable to another or to a constant using comparison operators

    • == equals

    • < less than

    • <= less than or equal to

    • != not equals

    • > greater than

    • >= greater than or equal to

Logical Expressions in Python


While loops

  • Indeterminant loop – use when duration of loop is unknown

  • Can be imbedded inside for loops

  • General while loop structure

    while logical_expression:

    # statements to run as long as logical_expression stays true

While Loops


Break statement

  • Can use to terminate a loop or part of a specific loop if a statement becomes true

  • Example of how break statement is used

    x = 0

    for x in xlist:

    if x >= 40:

    x += 1

    break

    else:

    x += 1

Break Statement


Lists

  • Collection of strings, floating point numbers, or integers listed in some order

  • Arrays are special form of list in which all elements are of same data type

  • Numeric Python module (numpy) is used to work with arrays

Lists


List operators

  • List – create a defined list-type object

    • x = list([4.0, ‘Hypsometric’, 34])

  • Range – returns list of integers in specified range – important in for loops

    • range(4) returns [0, 1, 2, 3]

    • range (2,4) returns [2, 3]

  • Len – counts how many numbers are in a list

    • len(range(2,4)) produces a value of 2

  • Sum – adds up the numbers in a list

List Operators


Line splitting

  • Input files consists of strings which can be split into component strings and then converted into numbers

  • Split method is used to break strings into more useful components

  • Default separator is a blank space, but separators can be anything, such as , : ; / -

  • Line splitting most useful when done inside a loop

    • Line = “32, 32.4, 36.8, Freezing Points”

    • q = float(line.split(“,”)[2]) = 36.8

Line Splitting


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