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# Python - PowerPoint PPT Presentation

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

Spacing

• 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
• Indenting in loops – no end statement
• Capitalization matters – Temp, temp, tEmp, TEMP are all different variables
Python Basics

Mathematical expressions are the same

• - Subtraction
• * Multiplication
• / Division
• ** Exponentiation
• 9.8E-8 = 9.8 * (10 ** (-8))
Numerical Arithmetic

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
• 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

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

• Average /= linecount==> average = average / linecount
• Balance -= payment ==> balance = balance – payment
• Population *= growth ==> population = population * growth
Shortcut Operators

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

• 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

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
• 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

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

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

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

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

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 – 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

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