Other Icon-Click Limitations

Even with the input trick, clicking file icons is not without its perils. You also may not get to see Python error messages. If your script generates an error, the error message text is written to the pop-up console window—which then immediately disappears! Worse, adding an input call to your file will not help this time because your script will likely abort long before it reaches this call. In other words, you won’t be able to tell what went wrong.

Because of these limitations, it is probably best to view icon clicks as a way to launch programs after they have been debugged or have been instrumented to write their output to a file. Especially when starting out, use other techniques—such as system command lines and IDLE (discussed further in the section The IDLE User Interface)—so that you can see generated error messages and view your normal output without resorting to coding tricks. When we discuss exceptions later in this book, you’ll also learn that it is possible to intercept and recover from errors so that they do not terminate your programs. Watch for the discussion of the try statement later in this book for an alternative way to keep the console window from closing on errors.

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[6] It is also possible to completely suppress the pop-up DOS console window for clicked files on Windows. Files whose names end in a .pyw extension will display only windows constructed by your script, not the default DOS console window. .pyw files are simply .py source files that have this special operational behavior on Windows. They are mostly used for Python-coded user interfaces that build windows of their own, often in conjunction with various techniques for saving printed output and errors to files.