11
How do I run a Python program under Windows?
12
--------------------------------------------
14
This is not necessarily a straightforward question. If you are already familiar
15
with running programs from the Windows command line then everything will seem
16
obvious; otherwise, you might need a little more guidance. There are also
17
differences between Windows 95, 98, NT, ME, 2000 and XP which can add to the
20
.. sidebar:: |Python Development on XP|_
21
:subtitle: `Python Development on XP`_
23
This series of screencasts aims to get you up and running with Python on
24
Windows XP. The knowledge is distilled into 1.5 hours and will get you up
25
and running with the right Python distribution, coding in your choice of IDE,
26
and debugging and writing solid code with unit-tests.
28
.. |Python Development on XP| image:: python-video-icon.png
29
.. _`Python Development on XP`:
30
http://www.showmedo.com/videos/series?name=pythonOzsvaldPyNewbieSeries
32
Unless you use some sort of integrated development environment, you will end up
33
*typing* Windows commands into what is variously referred to as a "DOS window"
34
or "Command prompt window". Usually you can create such a window from your
35
Start menu; under Windows 2000 the menu selection is :menuselection:`Start -->
36
Programs --> Accessories --> Command Prompt`. You should be able to recognize
37
when you have started such a window because you will see a Windows "command
38
prompt", which usually looks like this::
42
The letter may be different, and there might be other things after it, so you
43
might just as easily see something like::
45
D:\Steve\Projects\Python>
47
depending on how your computer has been set up and what else you have recently
48
done with it. Once you have started such a window, you are well on the way to
49
running Python programs.
51
You need to realize that your Python scripts have to be processed by another
52
program called the Python interpreter. The interpreter reads your script,
53
compiles it into bytecodes, and then executes the bytecodes to run your
54
program. So, how do you arrange for the interpreter to handle your Python?
56
First, you need to make sure that your command window recognises the word
57
"python" as an instruction to start the interpreter. If you have opened a
58
command window, you should try entering the command ``python`` and hitting
59
return. You should then see something like::
61
Python 2.2 (#28, Dec 21 2001, 12:21:22) [MSC 32 bit (Intel)] on win32
62
Type "help", "copyright", "credits" or "license" for more information.
65
You have started the interpreter in "interactive mode". That means you can enter
66
Python statements or expressions interactively and have them executed or
67
evaluated while you wait. This is one of Python's strongest features. Check it
68
by entering a few expressions of your choice and seeing the results::
75
Many people use the interactive mode as a convenient yet highly programmable
76
calculator. When you want to end your interactive Python session, hold the Ctrl
77
key down while you enter a Z, then hit the "Enter" key to get back to your
78
Windows command prompt.
80
You may also find that you have a Start-menu entry such as :menuselection:`Start
81
--> Programs --> Python 2.2 --> Python (command line)` that results in you
82
seeing the ``>>>`` prompt in a new window. If so, the window will disappear
83
after you enter the Ctrl-Z character; Windows is running a single "python"
84
command in the window, and closes it when you terminate the interpreter.
86
If the ``python`` command, instead of displaying the interpreter prompt ``>>>``,
87
gives you a message like::
89
'python' is not recognized as an internal or external command,
90
operable program or batch file.
92
.. sidebar:: |Adding Python to DOS Path|_
93
:subtitle: `Adding Python to DOS Path`_
95
Python is not added to the DOS path by default. This screencast will walk
96
you through the steps to add the correct entry to the `System Path`, allowing
97
Python to be executed from the command-line by all users.
99
.. |Adding Python to DOS Path| image:: python-video-icon.png
100
.. _`Adding Python to DOS Path`:
101
http://showmedo.com/videos/video?name=960000&fromSeriesID=96
106
Bad command or filename
108
then you need to make sure that your computer knows where to find the Python
109
interpreter. To do this you will have to modify a setting called PATH, which is
110
a list of directories where Windows will look for programs.
112
You should arrange for Python's installation directory to be added to the PATH
113
of every command window as it starts. If you installed Python fairly recently
118
will probably tell you where it is installed; the usual location is something
119
like ``C:\Python23``. Otherwise you will be reduced to a search of your whole
120
disk ... use :menuselection:`Tools --> Find` or hit the :guilabel:`Search`
121
button and look for "python.exe". Supposing you discover that Python is
122
installed in the ``C:\Python23`` directory (the default at the time of writing),
123
you should make sure that entering the command ::
127
starts up the interpreter as above (and don't forget you'll need a "CTRL-Z" and
128
an "Enter" to get out of it). Once you have verified the directory, you need to
129
add it to the start-up routines your computer goes through. For older versions
130
of Windows the easiest way to do this is to edit the ``C:\AUTOEXEC.BAT``
131
file. You would want to add a line like the following to ``AUTOEXEC.BAT``::
133
PATH C:\Python23;%PATH%
135
For Windows NT, 2000 and (I assume) XP, you will need to add a string such as ::
139
to the current setting for the PATH environment variable, which you will find in
140
the properties window of "My Computer" under the "Advanced" tab. Note that if
141
you have sufficient privilege you might get a choice of installing the settings
142
either for the Current User or for System. The latter is preferred if you want
143
everybody to be able to run Python on the machine.
145
If you aren't confident doing any of these manipulations yourself, ask for help!
146
At this stage you may want to reboot your system to make absolutely sure the new
147
setting has taken effect. You probably won't need to reboot for Windows NT, XP
148
or 2000. You can also avoid it in earlier versions by editing the file
149
``C:\WINDOWS\COMMAND\CMDINIT.BAT`` instead of ``AUTOEXEC.BAT``.
151
You should now be able to start a new command window, enter ``python`` at the
152
``C:\>`` (or whatever) prompt, and see the ``>>>`` prompt that indicates the
153
Python interpreter is reading interactive commands.
155
Let's suppose you have a program called ``pytest.py`` in directory
156
``C:\Steve\Projects\Python``. A session to run that program might look like
159
C:\> cd \Steve\Projects\Python
160
C:\Steve\Projects\Python> python pytest.py
162
Because you added a file name to the command to start the interpreter, when it
163
starts up it reads the Python script in the named file, compiles it, executes
164
it, and terminates, so you see another ``C:\>`` prompt. You might also have
167
C:\> python \Steve\Projects\Python\pytest.py
169
if you hadn't wanted to change your current directory.
171
Under NT, 2000 and XP you may well find that the installation process has also
172
arranged that the command ``pytest.py`` (or, if the file isn't in the current
173
directory, ``C:\Steve\Projects\Python\pytest.py``) will automatically recognize
174
the ".py" extension and run the Python interpreter on the named file. Using this
175
feature is fine, but *some* versions of Windows have bugs which mean that this
176
form isn't exactly equivalent to using the interpreter explicitly, so be
179
The important things to remember are:
181
1. Start Python from the Start Menu, or make sure the PATH is set correctly so
182
Windows can find the Python interpreter. ::
186
should give you a '>>>' prompt from the Python interpreter. Don't forget the
187
CTRL-Z and ENTER to terminate the interpreter (and, if you started the window
188
from the Start Menu, make the window disappear).
190
2. Once this works, you run programs with commands::
192
python {program-file}
194
3. When you know the commands to use you can build Windows shortcuts to run the
195
Python interpreter on any of your scripts, naming particular working
196
directories, and adding them to your menus. Take a look at ::
200
if your needs are complex.
202
4. Interactive mode (where you see the ``>>>`` prompt) is best used for checking
203
that individual statements and expressions do what you think they will, and
204
for developing code by experiment.
207
How do I make Python scripts executable?
208
----------------------------------------
210
On Windows 2000, the standard Python installer already associates the .py
211
extension with a file type (Python.File) and gives that file type an open
212
command that runs the interpreter (``D:\Program Files\Python\python.exe "%1"
213
%*``). This is enough to make scripts executable from the command prompt as
214
'foo.py'. If you'd rather be able to execute the script by simple typing 'foo'
215
with no extension you need to add .py to the PATHEXT environment variable.
217
On Windows NT, the steps taken by the installer as described above allow you to
218
run a script with 'foo.py', but a longtime bug in the NT command processor
219
prevents you from redirecting the input or output of any script executed in this
220
way. This is often important.
222
The incantation for making a Python script executable under WinNT is to give the
223
file an extension of .cmd and add the following as the first line::
225
@setlocal enableextensions & python -x %~f0 %* & goto :EOF
228
Why does Python sometimes take so long to start?
229
------------------------------------------------
231
Usually Python starts very quickly on Windows, but occasionally there are bug
232
reports that Python suddenly begins to take a long time to start up. This is
233
made even more puzzling because Python will work fine on other Windows systems
234
which appear to be configured identically.
236
The problem may be caused by a misconfiguration of virus checking software on
237
the problem machine. Some virus scanners have been known to introduce startup
238
overhead of two orders of magnitude when the scanner is configured to monitor
239
all reads from the filesystem. Try checking the configuration of virus scanning
240
software on your systems to ensure that they are indeed configured identically.
241
McAfee, when configured to scan all file system read activity, is a particular
245
Where is Freeze for Windows?
246
----------------------------
248
"Freeze" is a program that allows you to ship a Python program as a single
249
stand-alone executable file. It is *not* a compiler; your programs don't run
250
any faster, but they are more easily distributable, at least to platforms with
251
the same OS and CPU. Read the README file of the freeze program for more
254
You can use freeze on Windows, but you must download the source tree (see
255
http://www.python.org/download/source). The freeze program is in the
256
``Tools\freeze`` subdirectory of the source tree.
258
You need the Microsoft VC++ compiler, and you probably need to build Python.
259
The required project files are in the PCbuild directory.
262
Is a ``*.pyd`` file the same as a DLL?
263
--------------------------------------
265
.. XXX update for py3k (PyInit_foo)
267
Yes, .pyd files are dll's, but there are a few differences. If you have a DLL
268
named ``foo.pyd``, then it must have a function ``initfoo()``. You can then
269
write Python "import foo", and Python will search for foo.pyd (as well as
270
foo.py, foo.pyc) and if it finds it, will attempt to call ``initfoo()`` to
271
initialize it. You do not link your .exe with foo.lib, as that would cause
272
Windows to require the DLL to be present.
274
Note that the search path for foo.pyd is PYTHONPATH, not the same as the path
275
that Windows uses to search for foo.dll. Also, foo.pyd need not be present to
276
run your program, whereas if you linked your program with a dll, the dll is
277
required. Of course, foo.pyd is required if you want to say ``import foo``. In
278
a DLL, linkage is declared in the source code with ``__declspec(dllexport)``.
279
In a .pyd, linkage is defined in a list of available functions.
282
How can I embed Python into a Windows application?
283
--------------------------------------------------
285
Embedding the Python interpreter in a Windows app can be summarized as follows:
287
1. Do _not_ build Python into your .exe file directly. On Windows, Python must
288
be a DLL to handle importing modules that are themselves DLL's. (This is the
289
first key undocumented fact.) Instead, link to :file:`python{NN}.dll`; it is
290
typically installed in ``C:\Windows\System``. NN is the Python version, a
291
number such as "23" for Python 2.3.
293
You can link to Python statically or dynamically. Linking statically means
294
linking against :file:`python{NN}.lib`, while dynamically linking means
295
linking against :file:`python{NN}.dll`. The drawback to dynamic linking is
296
that your app won't run if :file:`python{NN}.dll` does not exist on your
297
system. (General note: :file:`python{NN}.lib` is the so-called "import lib"
298
corresponding to :file:`python.dll`. It merely defines symbols for the
301
Linking dynamically greatly simplifies link options; everything happens at
302
run time. Your code must load :file:`python{NN}.dll` using the Windows
303
``LoadLibraryEx()`` routine. The code must also use access routines and data
304
in :file:`python{NN}.dll` (that is, Python's C API's) using pointers obtained
305
by the Windows ``GetProcAddress()`` routine. Macros can make using these
306
pointers transparent to any C code that calls routines in Python's C API.
308
Borland note: convert :file:`python{NN}.lib` to OMF format using Coff2Omf.exe
311
2. If you use SWIG, it is easy to create a Python "extension module" that will
312
make the app's data and methods available to Python. SWIG will handle just
313
about all the grungy details for you. The result is C code that you link
314
*into* your .exe file (!) You do _not_ have to create a DLL file, and this
315
also simplifies linking.
317
3. SWIG will create an init function (a C function) whose name depends on the
318
name of the extension module. For example, if the name of the module is leo,
319
the init function will be called initleo(). If you use SWIG shadow classes,
320
as you should, the init function will be called initleoc(). This initializes
321
a mostly hidden helper class used by the shadow class.
323
The reason you can link the C code in step 2 into your .exe file is that
324
calling the initialization function is equivalent to importing the module
325
into Python! (This is the second key undocumented fact.)
327
4. In short, you can use the following code to initialize the Python interpreter
328
with your extension module.
334
Py_Initialize(); // Initialize Python.
335
initmyAppc(); // Initialize (import) the helper class.
336
PyRun_SimpleString("import myApp") ; // Import the shadow class.
338
5. There are two problems with Python's C API which will become apparent if you
339
use a compiler other than MSVC, the compiler used to build pythonNN.dll.
341
Problem 1: The so-called "Very High Level" functions that take FILE *
342
arguments will not work in a multi-compiler environment because each
343
compiler's notion of a struct FILE will be different. From an implementation
344
standpoint these are very _low_ level functions.
346
Problem 2: SWIG generates the following code when generating wrappers to void
352
_resultobj = Py_None;
355
Alas, Py_None is a macro that expands to a reference to a complex data
356
structure called _Py_NoneStruct inside pythonNN.dll. Again, this code will
357
fail in a mult-compiler environment. Replace such code by:
361
return Py_BuildValue("");
363
It may be possible to use SWIG's ``%typemap`` command to make the change
364
automatically, though I have not been able to get this to work (I'm a
365
complete SWIG newbie).
367
6. Using a Python shell script to put up a Python interpreter window from inside
368
your Windows app is not a good idea; the resulting window will be independent
369
of your app's windowing system. Rather, you (or the wxPythonWindow class)
370
should create a "native" interpreter window. It is easy to connect that
371
window to the Python interpreter. You can redirect Python's i/o to _any_
372
object that supports read and write, so all you need is a Python object
373
(defined in your extension module) that contains read() and write() methods.
376
How do I use Python for CGI?
377
----------------------------
379
On the Microsoft IIS server or on the Win95 MS Personal Web Server you set up
380
Python in the same way that you would set up any other scripting engine.
382
Run regedt32 and go to::
384
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W3SVC\Parameters\ScriptMap
386
and enter the following line (making any specific changes that your system may
389
.py :REG_SZ: c:\<path to python>\python.exe -u %s %s
391
This line will allow you to call your script with a simple reference like:
392
``http://yourserver/scripts/yourscript.py`` provided "scripts" is an
393
"executable" directory for your server (which it usually is by default). The
394
:option:`-u` flag specifies unbuffered and binary mode for stdin - needed when
395
working with binary data.
397
In addition, it is recommended that using ".py" may not be a good idea for the
398
file extensions when used in this context (you might want to reserve ``*.py``
399
for support modules and use ``*.cgi`` or ``*.cgp`` for "main program" scripts).
401
In order to set up Internet Information Services 5 to use Python for CGI
402
processing, please see the following links:
404
http://www.e-coli.net/pyiis_server.html (for Win2k Server)
405
http://www.e-coli.net/pyiis.html (for Win2k pro)
407
Configuring Apache is much simpler. In the Apache configuration file
408
``httpd.conf``, add the following line at the end of the file::
410
ScriptInterpreterSource Registry
412
Then, give your Python CGI-scripts the extension .py and put them in the cgi-bin
416
How do I keep editors from inserting tabs into my Python source?
417
----------------------------------------------------------------
419
The FAQ does not recommend using tabs, and the Python style guide, :pep:`8`,
420
recommends 4 spaces for distributed Python code; this is also the Emacs
423
Under any editor, mixing tabs and spaces is a bad idea. MSVC is no different in
424
this respect, and is easily configured to use spaces: Take :menuselection:`Tools
425
--> Options --> Tabs`, and for file type "Default" set "Tab size" and "Indent
426
size" to 4, and select the "Insert spaces" radio button.
428
If you suspect mixed tabs and spaces are causing problems in leading whitespace,
429
run Python with the :option:`-t` switch or run ``Tools/Scripts/tabnanny.py`` to
430
check a directory tree in batch mode.
433
How do I check for a keypress without blocking?
434
-----------------------------------------------
436
Use the msvcrt module. This is a standard Windows-specific extension module.
437
It defines a function ``kbhit()`` which checks whether a keyboard hit is
438
present, and ``getch()`` which gets one character without echoing it.
441
How do I emulate os.kill() in Windows?
442
--------------------------------------
447
"""kill function for Win32"""
449
handle = win32api.OpenProcess(1, 0, pid)
450
return (0 != win32api.TerminateProcess(handle, 0))
453
Why does os.path.isdir() fail on NT shared directories?
454
-------------------------------------------------------
456
The solution appears to be always append the "\\" on the end of shared
460
>>> os.path.isdir( '\\\\rorschach\\public')
462
>>> os.path.isdir( '\\\\rorschach\\public\\')
465
It helps to think of share points as being like drive letters. Example::
467
k: is not a directory
469
k:\media is a directory
470
k:\media\ is not a directory
472
The same rules apply if you substitute "k:" with "\\conky\foo"::
474
\\conky\foo is not a directory
475
\\conky\foo\ is a directory
476
\\conky\foo\media is a directory
477
\\conky\foo\media\ is not a directory
480
cgi.py (or other CGI programming) doesn't work sometimes on NT or win95!
481
------------------------------------------------------------------------
483
Be sure you have the latest python.exe, that you are using python.exe rather
484
than a GUI version of Python and that you have configured the server to execute
487
"...\python.exe -u ..."
489
for the CGI execution. The :option:`-u` (unbuffered) option on NT and Win95
490
prevents the interpreter from altering newlines in the standard input and
491
output. Without it post/multipart requests will seem to have the wrong length
492
and binary (e.g. GIF) responses may get garbled (resulting in broken images, PDF
493
files, and other binary downloads failing).
496
Why doesn't os.popen() work in PythonWin on NT?
497
-----------------------------------------------
499
The reason that os.popen() doesn't work from within PythonWin is due to a bug in
500
Microsoft's C Runtime Library (CRT). The CRT assumes you have a Win32 console
501
attached to the process.
503
You should use the win32pipe module's popen() instead which doesn't depend on
504
having an attached Win32 console.
509
f = win32pipe.popen('dir /c c:\\')
514
Why doesn't os.popen()/win32pipe.popen() work on Win9x?
515
-------------------------------------------------------
517
There is a bug in Win9x that prevents os.popen/win32pipe.popen* from
518
working. The good news is there is a way to work around this problem. The
519
Microsoft Knowledge Base article that you need to lookup is: Q150956. You will
520
find links to the knowledge base at: http://support.microsoft.com/.
523
PyRun_SimpleFile() crashes on Windows but not on Unix; why?
524
-----------------------------------------------------------
526
This is very sensitive to the compiler vendor, version and (perhaps) even
527
options. If the FILE* structure in your embedding program isn't the same as is
528
assumed by the Python interpreter it won't work.
530
The Python 1.5.* DLLs (``python15.dll``) are all compiled with MS VC++ 5.0 and
531
with multithreading-DLL options (``/MD``).
533
If you can't change compilers or flags, try using :cfunc:`Py_RunSimpleString`.
534
A trick to get it to run an arbitrary file is to construct a call to
535
:func:`execfile` with the name of your file as argument.
537
Also note that you can not mix-and-match Debug and Release versions. If you
538
wish to use the Debug Multithreaded DLL, then your module *must* have an "_d"
539
appended to the base name.
542
Importing _tkinter fails on Windows 95/98: why?
543
------------------------------------------------
545
Sometimes, the import of _tkinter fails on Windows 95 or 98, complaining with a
546
message like the following::
548
ImportError: DLL load failed: One of the library files needed
549
to run this application cannot be found.
551
It could be that you haven't installed Tcl/Tk, but if you did install Tcl/Tk,
552
and the Wish application works correctly, the problem may be that its installer
553
didn't manage to edit the autoexec.bat file correctly. It tries to add a
554
statement that changes the PATH environment variable to include the Tcl/Tk 'bin'
555
subdirectory, but sometimes this edit doesn't quite work. Opening it with
556
notepad usually reveals what the problem is.
558
(One additional hint, noted by David Szafranski: you can't use long filenames
559
here; e.g. use ``C:\PROGRA~1\Tcl\bin`` instead of ``C:\Program Files\Tcl\bin``.)
562
How do I extract the downloaded documentation on Windows?
563
---------------------------------------------------------
565
Sometimes, when you download the documentation package to a Windows machine
566
using a web browser, the file extension of the saved file ends up being .EXE.
567
This is a mistake; the extension should be .TGZ.
569
Simply rename the downloaded file to have the .TGZ extension, and WinZip will be
570
able to handle it. (If your copy of WinZip doesn't, get a newer one from
571
http://www.winzip.com.)
574
Missing cw3215mt.dll (or missing cw3215.dll)
575
--------------------------------------------
577
Sometimes, when using Tkinter on Windows, you get an error that cw3215mt.dll or
578
cw3215.dll is missing.
580
Cause: you have an old Tcl/Tk DLL built with cygwin in your path (probably
581
``C:\Windows``). You must use the Tcl/Tk DLLs from the standard Tcl/Tk
582
installation (Python 1.5.2 comes with one).
585
Warning about CTL3D32 version from installer
586
--------------------------------------------
588
The Python installer issues a warning like this::
590
This version uses ``CTL3D32.DLL`` which is not the correct version.
591
This version is used for windows NT applications only.
595
This is a Microsoft DLL, and a notorious source of problems. The message
596
means what it says: you have the wrong version of this DLL for your operating
597
system. The Python installation did not cause this -- something else you
598
installed previous to this overwrote the DLL that came with your OS (probably
599
older shareware of some sort, but there's no way to tell now). If you search
600
for "CTL3D32" using any search engine (AltaVista, for example), you'll find
601
hundreds and hundreds of web pages complaining about the same problem with
602
all sorts of installation programs. They'll point you to ways to get the
603
correct version reinstalled on your system (since Python doesn't cause this,
606
David A Burton has written a little program to fix this. Go to
607
http://www.burtonsys.com/downloads.html and click on "ctl3dfix.zip".
added
removed
Doc/faq/windows.rst
