2 Python Programming Environment We will use the “PythonWin” version 2.7 systemThis programming environment includes a code editor and a code interpreterA code interpreter executes statements line-by-line as you type them – very useful for testingA Code editor is used to type a complete program that is later tested and “de-bugged”
3 PythonWin Environment Interpreter window is displayed first.You can type and execute simple statements in this window.
4 PythonWin Environment To type a Python script program select “File > New > Script”.Type in code and save with a .py extention.A good idea to have a folder such as “\PythonProgs\” just for source code scripts.
5 PythonWin Environment To load an existing python script select “File > Open” to load script into an edit window.
6 PythonWin Environment To run a script you should load it, and then select “File > Run”Note that you may enter “command line arguments” at this point if neededSelect “OK” button to run the script
7 Python Programming Fundamentals Google “Python Language Reference” to load this help file
8 Python Data Types String: a sequence of alphanumeric characters Integer: a whole number that has no fractional componentFloat: a number that contains a fractional componentString example: “105 Glendale Avenue” (note that strings are enclosed in quotes)Integer examples: 100, -19, 0,Float examples: 1.0, , E3
9 Python Assignment Statement The “=“ sign is the assignment operator as it is in most programming languagesX = 1Print X # the number “1” will appear on the screenX = X + 5Print X # the number “6” will appear on the screen
10 Python Comments A python comment begins with a “#”. Anything after the “#” is ignored by PythonThe 1st line in the below script is a comment line- it is ignored by PythonThe characters to the right of the “#” on lines 2-5 are ignored# get x1, y1, x2, y2 from the command linex1param = float(StripComma(sys.argv)) # x1y1param = float(StripComma(sys.argv)) # y1x2param = float(StripComma(sys.argv)) # x2y2param = float(StripComma(sys.argv)) # y2
11 Python Operators (in order of precedence) Multiplication: *Division: /Modulus: %Addition: +Subtraction: -
12 ExpressionsExpressions are combinations of data and operators:
13 Built-in Python Functions A function takes an “argument” or “arguments” and returns a value that can be used in an assignment statementIn the below satements abs(x) and pow(x,y) are built-in functions in every implementation of the Python languagex = abs(-8)print x # the number “8” would appear in the interactive windowy = pow(2,3)print y # the number “8” would appear in the interactive window
14 Python Built-In Functions abs(x) # returns the absolute value of xfloat(x) # returns the string x converted to a floating point numberint(x) # returns the string x converted to a integer numberpow(x,y) # returns the number x rasied to the y powerround(x,n) # rounds the number x to n decimal placesstr(x) # returns the string equivalent of the object x
15 More Complex Expressions using Functions and Exponentiation Note that trig functions use radian angular values.You must convert degrees to radians before using the trig functions ( radians = degrees * /180.0).Note that before using the trig functions the math “module” had to be imported.
16 Controlling Program Flow: Conditional Statements A statement uses “reserved” python language words to initiate an actionA conditional statement makes a decision at run-timeX = 10If x == 10 :print “X=10”Note: everything indentedBelow the “If” statement isPart of the statement.
17 Conditional Statements: More Complex IF/ELIF/ELSE construct The “elif” and “else” keywords can be used to construct more complex decision structuresx = random.randint(1,10)If x == 1 :print “you are in first place”Elif x == 2 :print “you are in second place”Elif x == 3 :print “you are in third place”Else :print “ sorry, you didn’t place this time”
18 Controlling program flow with a loop: While statement While statements can be used to repeat a section of code until some condition is reached.i = 0While i <= 10 :print Ii = i + 1# you could also use i += 1
19 For LoopsA “For” loop uses a “list”. First a list must be built before it can be used in the For loopMylist = [“A”, “B”, “C”, “D”]For letter in Mylist :print letter # the letters “A” through “D” would print to the screen
20 Getting User Input: command line Command line parameters are entered at run time in the “Run Script” window
21 Getting User Input: “Input” function The “input” function prompts the user for input during the running of the script
22 User Input: Input function Note that if you use the “input” function and you enter a string value it must be enclosed in quotes (single or double).
23 FunctionsA function is a stand-alone section of code that is designed to accomplish a specific task based on one or more parameters passed to the functionThe function returns a calculated result so a function normally appears in the main code to the right of an assignment (=) statement so the returned value is stored in the variable on the left side of the assignment statement
24 Function PlacementFunctions are normally placed at the top of the main program file because they need to be defined before they are referenced in the main programBelow is an example function that converts a longitude string value (“ ”) to its decimal degree number equivalent