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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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Presentation Transcript
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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