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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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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

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

General Programming Tips

Python Basics

Numerical Arithmetic

• Built-in functions initially

• 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

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

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

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

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

Shortcut Operators

Input/Output

• Reading input files writeable (output) 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

• Types: for, if, while loops writeable (output) files

• 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

• Used to make logical decisions program to run

• 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

While Loops

Break Statement

Lists

• List – create a defined list-type object listed in some order

• 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