《Introduction to Python》由会员分享，可在线阅读，更多相关《Introduction to Python（25页珍藏版）》请在金锄头文库上搜索。
1、Introduction to Python,Introduction to Python,Python is a high-level programming language Open source and community driven “Batteries Included” a standard distribution includes many modules Dynamic typed Source can be compiled or run just-in-time Similar to perl, tcl, ruby,Why Python?,Unlike AML and
2、 Avenue, there is a considerable base of developers already using the language “Tried and true” language that has been in development since 1991 Can interface with the Component Object Model (COM) used by Windows Can interface with Open Source GIS toolsets,Why not Visual Basic?,Visual Basic is still
3、 the method of configuring and customizing ArcMap If you have a button on the toolbar, its VB Python scripts can be placed in ArcToolbox Python can be run from the command line without ArcMap or ArcCatalog being open Using just the GIS Engine, lower overhead Rapid prototyping, ease of authoring, etc
4、.,Python Interfaces,IDLE a cross-platform Python development environment PythonWin a Windows only interface to Python Python Shell running python from the Command Line opens this interactive shell For the exercises, well use IDLE, but you can try them all and pick a favorite,IDLE Development Environ
5、ment,IDLE helps you program in Python by: color-coding your program code debugging auto-indent interactive shell,Example Python,Hello World print “hello world” Prints hello world to standard out Open IDLE and try it out yourself Follow along using IDLE,More than just printing,Python is an object ori
6、ented language Practically everything can be treated as an object “hello world” is a string Strings, as objects, have methods that return the result of a function on the string,String Methods,Assign a string to a variable In this case “hw” hw.title() hw.upper() hw.isdigit() hw.islower(),String Metho
7、ds,The string held in your variable remains the same The method returns an altered string Changing the variable requires reassignment hw = hw.upper() hw now equals “HELLO WORLD”,Other Python Objects,Lists (mutable sets of strings) var = # create list var = one, 2, three, banana Tuples (immutable set
8、s) var = (one, 2, three, banana) Dictionaries (associative arrays or hashes) var = # create dictionary var = lat: 40.20547, lon: -74.76322 varlat = 40.2054 Each has its own set of methods,Lists,Think of a list as a stack of cards, on which your information is written The information stays in the ord
9、er you place it in until you modify that order Methods return a string or subset of the list or modify the list to add or remove components Written as varindex, index refers to order within set (think card number, starting at 0) You can step through lists as part of a loop,List Methods,Adding to the
10、 List varn = object replaces n with object var.append(object) adds object to the end of the list Removing from the List varn = empties contents of card, but preserves order var.remove(n) removes card at n var.pop(n) removes n and returns its value,Lists in ArcToolbox,You will create lists: Layers as
11、 inputs Attributes to match Arrays of objects You will work with lists: List of field names List of selected features,Tuples,Like a list, tuples are iterable arrays of objects Tuples are immutable once created, unchangeable To add or remove items, you must redeclare Example uses of tuples County Nam
12、es Land Use Codes Ordered set of functions,Dictionaries,Dictionaries are sets of key & value pairs Allows you to identify values by a descriptive name instead of order in a list Keys are unordered unless explicitly sorted Keys are unique: varitem = “apple” varitem = “banana” print varitem prints jus
13、t banana,Indentation and Blocks,Python uses whitespace and indents to denote blocks of code Lines of code that begin a block end in a colon: Lines within the code block are indented at the same level To end a code block, remove the indentation Youll want blocks of code that run only when certain con
14、ditions are met,Conditional Branching,if and else if variable = condition: #do something based on v = c else:#do something based on v != c elif allows for additional branching if condition: elif another condition: else: #none of the above,Looping with For,For allows you to loop over a block of code
15、a set number of times For is great for manipulating lists:a = cat, window, defenestrate for x in a: print x, len(x)Results: cat 3 window 6 defenestrate 12,Looping with For,We could use a for loop to perform geoprocessing tasks on each layer in a list We could get a list of features in a feature clas
16、s and loop over each, checking attributes Anything in a sequence or list can be used in a For loop Just be sure not to modify the list while looping,Modules,Modules are additional pieces of code that further extend Pythons functionality A module typically has a specific function additional math functions, databases, network Python comes with many useful modules arcgisscripting is the module we will use to load ArcGIS toolbox functions into Python,
