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Visual Python Tutorial

Version 1.8.3 Table of Contents Introduction Open the Visual Python Tutorial Solutions and Projects Run the Program Edit the Program Task List Syntax Checking Syntax Coloring Method and Module Tips Call Tips Dynamic Help Code Folding Smart Indenting Commenting Blocks of Code Opening a Module Debug the Program Setting Breakpoints Viewing and Changing Variables Using the Call Stack

ASPN, the ActiveState Programmer Network, features comprehensive Python programming resources. Check out: The Python Cookbook, a collaborative library of Python code samples and snippets.

Introduction

Visual Python is ActiveState's full-featured Python plug-in for Visual Studio .NET. Developers who are familiar with Visual Studio can use the same powerful tool set and intuitive environment to write Python programs. This tutorial is an introduction to Visual Python. Using the sample solution included with Visual Python, follow the tutorial by performing the instructions in the Try it Out sections.

Open the Visual Python Tutorial

The tutorial uses the sample solution "Dramatis Personae" included with Visual Python. In the editing section of the tutorial, you will alter the program to display Visual Python's editing features. Instructions for reverting the changes are included in the relevant tutorial sections.

1. From the Windows Start menu, select Start|Programs|ActiveState Visual Python|Samples|Dramatis Personae. This will load Visual Studio, and open the sample project in Visual Studio's Solution Explorer. (If you have previously opened the sample project, the files may open automatically in the editor, as Visual Studio stores the state of each solution in memory.)
2. If necessary, in the Solution Explorer window, double click python_sample.py to open the file in the Visual Studio editor pane. If the Solution Explorer is not visible, select View|Solution Explorer.
3. Throughout the tutorial, sections of the program are referred to by the line number. If necessary, enable the display of line numbers in Visual Studio by selecting Tools|Options|Text Editor and checking the Line numbers box in the Display section of the dialog.

By default, Visual Python's editing features are enabled when the program is installed. However, if you have previously disabled any of the features, you will be instructed to re-enable them in the relevant section of the tutorial.

Solutions and Projects

In Visual Studio, the "solution" is the top level of project organization. Solutions contain one or more projects; projects contain one or more "items" (files, folders, data connections, etc.)

• solutions can contain multiple projects
• projects can contain multiple items
• use the Solution Explorer (View|Solution Explorer) to modify the properties and contents of solutions and projects
• in the Solution Explorer, right-click the solution, project or file name for a context menu
• when a solution has multiple projects, the project name that is displayed in bold text is the "Startup Project"

Try it Out if necessary, open the Dramatis Personae solution View the Dramatis Personae solution in the Solution Explorer (View|Solution Explorer). the "dramatis personae" project is contained in the "dramatis personae" solution the "python_sample.py" program and the "dream_act1.xml" data file are contained in the "dramatis personae" project

Run the Program

In this step, you will simply run the program to see what it does.

• programs can be run within Visual Studio's Output window, or within a shell window
• to configure your run preference, check Run in shell window in the Project's Properties

Try it Out Select Debug|Start Without Debugging, or press Ctrl+F5. Visual Studio's Run Window displays the output from the program

Edit the Program

Task List

Visual Studio's Task List maintains a dynamic list of syntax errors in your Python program. (See Syntax Checking for more information.) To view a complete Task List, select View|Show Tasks|All.

• If the Task List window is not visible, select View|Other Windows|Task List to display it
• syntax errors are automatically added to the Task List
• when syntax errors are repaired, the items are removed from the Task List
• manual entries can be also added to the Task List
• comments prefixed with the text TODO: are added to the Task List

Try it Out Line 32: add the text #TODO: this is a comment the comment will be displayed in the Task List Clear the contents of line 32. Line 31: remove the bracket following name a syntax error is added to the Task List Re-enter the bracket following name.

Syntax Checking

Visual Python's syntax checking monitors the validity of your code as you type. To enable syntax checking, select Tools|Options|Text Editor|Python|Visual Python Specific, and ensure that the Check syntax while editing box is checked.

• syntax errors are underlined with red wavy lines
• explanatory pop-up tips are displayed when you hover the mouse pointer over the syntax error
• syntax errors are added to Visual Studio's Task List (View|Show Tasks|All)

Try it Out Line 8: delete a letter from the statement import line 8 is underlined to indicate a syntax error an explanatory message is displayed when you hover the cursor over the error an entry is added to the Task List Undo the change to Line 8.

Syntax Coloring

Syntax coloring displays different language elements in different colors. To configure custom colors, select Tools|Options|Environment|Fonts and Colors.

Things to Note

• When different languages share the same elements, the same color configuration is used for multiple languages. For example, the color assigned to the "Comment" language element will be applied to comments in programs of all languages supported by Visual Studio.

Try it Out Select Tools|Options|Environment|Fonts and Colors. Ensure that Text Editor is displayed in the "Show settings for" field. In the "Display Items" list, select Comment. Change the color in the "Item foreground" field to Green, and the "Item background" to Dark gray. Click OK.

Method and Module Tips

When you enter a space after the "import" or "from" command, Visual Python displays a list of folders and modules found in the system's PYTHONPATH environment variable, and in the directory where Visual Python was invoked. When you enter a period after a module name, a list of the classes and functions contained in the module is displayed. When you enter a period after a class name, a list of the methods within the class is displayed.

• to position the tip list, continue to enter the letters of the desired item
• to select an item, highlight it in the list box and press Enter or Tab
• to clear the tip list, press Esc
• to re-display the tip list, press Ctrl+J

Try it Out Line 9: enter import, followed by a space a list of folders and modules is displayed Line 9: enter xm and press Enter the xml folder will be inserted Line 9: enter a period after xml folders under the xml folder are displayed; select dom Line 9: enter a period after dom methods within the dom module are displayed Clear the contents of Line 9.

Call Tips

Call tips display the arguments, default values and a brief description for methods and functions. Call tips are displayed when you enter an open parenthesis ("(") after a module name followed by a function name, a class name followed by a method name, or a variable name followed by a method name.

• each argument is displayed in bold text as you complete the list of arguments
• to clear the tip, continue typing or press Esc
• to redisplay the tip, enter Ctrl+Shift+Space

Try it Out Line 9: enter import string Line 10: enter print string.join enter an open parenthesis - the string.join call tip is displayed Line 10: enter string.split enter an open parenthesis - the string.split call tip is displayed Clear the contents of lines 9 and 10.

Dynamic Help

Visual Studio's Dynamic Help pane displays links to context-sensitive Python language reference. To display the Dynamic Help pane, select Help|Dynamic Help.

• links to help topics are displayed based on the current cursor position
• to view and search the entire contents of the Python language reference, select Help|Contents|ActiveState Visual Python|Python Language Reference

Try it Out Line 17: click on the print keyword the print keyword is displayed in the Help list

Code Folding

Code folding is used to collapse and expand sections of your Python program. To display code folding markers, select Tools|Options|Text Editor|Python|Visual Python Specific, and ensure that the Show code folding box is checked.

• plus and minus symbols to the left of a line of code indicate sections that can be collapsed or expanded
• hover the mouse pointer over the box to the right of a folded line to display the folded code in a pop-up box
• collapsed blocks will be automatically expanded during debugging

Try it Out Line 27: click on the minus symbol lines 27 to 31 are collapsed a plus symbol to the left of line 27 indicates a collapsed block hover the mouse pointer over the three ellipses to the right of line 27 to display the hidden code

Smart Indenting

Smart indenting automatically indents lines in the editor after a colon. To enable Smart Indenting, select Tools|Options|Text Editor|Python|Tabs, and ensure that the "Smart" button is selected in the Indenting section of the dialog.

Things to Note

• after a colon, the indentation is incremented based on the value specified in the Tabs dialog of Visual Studio's Options

Visual Python also performs automatic indenting when a line break is entered after an open parenthesis. Visual Python sets the indentation level to the column following the parenthesis on the previous line. The close parenthesis will return the indentation to its previous level.

Things to Note

• indentation is incremented and decremented in the same manner as smart indenting, described above
• the indentation behavior will work for nested parentheses

Try it Out Line 29: at the end of the line, press Enter. the cursor position is indented by the amount specified for Tab values Line 25: after the open parenthesis, press Enter. the cursor position is indented to the column after the open parenthesis Undo the changes made to lines 25 and 29.

Commenting Blocks of Code

When you need to comment a selection of code, rather than an individual line, you can use Visual Studio's Comment Selection function.

• select the code block first
• to comment the selected block, click Edit|Advanced|Comment Selection, or use the keyboard shortcuts Ctrl+K, Ctrl+C
• to uncomment a commented block click Edit|Advanced|Uncomment Selection, or use the keyboard shortcuts Ctrl+K, Ctrl+U

Try it Out Line 27: click and drag from the beginning of line 27 to the end of line 31. Select Edit|Advanced|Comment Selection. each line of the block will be preceded by a # symbol Select Edit|Advanced|Uncomment Selection to remove the commenting.

Opening a Module

If your program includes an external Python module, you can open the module in the editor pane using the Open Document option on the right-mouse context menu. To open a module, position the cursor over the module name and right-click.

Try it Out Line 6: click anywhere in the text "import xml.dom.minidom". the "minidom.py" module will be opened in the editor pane

Debug the Program

In this section, you will analyze the program as it runs - that is, you'll debug it. The debug process can be used to identify and fix errors in programs; it is also useful for tracing the structure and functionality of existing programs.

Setting Breakpoints

Breakpoints can be manipulated in the breakpoint margin of the editor pane, or in the Breakpoints Window (Debug|Windows|Breakpoints (Ctrl+Alt+B)).

• click on the desired line in the breakpoint margin to set a breakpoint
• click on an existing breakpoint to remove it
• alternatively, use the Breakpoints Window to add and remove breakpoints

Try it Out Line 23: click on the grey margin to the left of the editor pane a red circle on the breakpoint margin indicates the breakpoint the breakpoint is added to the Breakpoints Window

Viewing and Changing Variables

Use the Watch window (Debug|Windows|Watch, or Ctrl+Alt+W number) to view and change variable values, and to add new variables. To add a variable to the Watch Window, copy and paste the variable from the editor pane or from the Locals window, or enter it manually.

Try it Out Select Debug|Start or press F5 to run the debugger. The program will run until it encounters the breakpoint on line 23 (set in the previous step). Display a Watch window by selecting Debug|Windows|Watch. Copy the variable element.childNodes[0].nodeValue on line 23 from the editor pane to the Watch window and press Enter. the variable value is displayed in the Watch Window

Using the Call Stack

The Call Stack (Debug|Windows|Call Stack or Ctrl+Alt+C) displays the name and language of each function that is currently on the stack. The variables displayed in the Locals window are particular to the stack; that is, you can see variables associated with each function by selecting the desired stack.

Try it Out If necessary, select Debug|Stop Debugging (Shift+F5) to stop the debugger. Set a breakpoint on line 11, then press F5 to run the debugger. When the debugger stops on line 11, press F11 to step into the next line. Display the Call Stack window by selecting Debug|Windows|Call Stack. the current stack is indicated by a yellow arrow double-click the python_sample.py stack; the editor pane will display the position where the stack changed, and the Locals window will display variables associated with that stack

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