🌐 Mailman 3 September 2000 - Python-list - python.org

Writing to locals(), globals(), and vars()
by Michael Haggerty Sept. 3, 2000

Sept. 3, 2000

First question: Is there a way to write to the local symbol table in a generic way (without using `exec')? For example, this could be used to return values from a database query: db.StoreRowToDict(storeto=locals()) # DOESN'T WORK! or locals().update(db.FetchRowAsDict()) # DOESN'T WORK! Neither can work because one cannot write to locals(). I quote from the Python Library Reference: locals() Return a dictionary representing the current local symbol table. Warning: the contents of this dictionary should not be modified; changes may not affect the values of local variables used by the interpreter. The same caveat is listed for the built-in function vars(). Second question: Is it legal to write to globals()? The Library Reference is mute on this point. (Not that it would help with the above problem...) Thanks, Michael -- Michael Haggerty mhagger(a)alum.mit.edu

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Newbie Question - String Input
by celtic＠ix.net.au Sept. 3, 2000

Sept. 3, 2000

I am using Python on a Wintel machine and I am trying to get Python to accept string data. In the following program (a very basic program) Python accepts numerical data without any problems but will not accept any string data at all - the program crashes with the following error: Traceback (innermost last): File "hello.py", line9, in ? userName=input("What is your name? ") File "<string>", in line 0, in ? NameError: whatever_I_Entered Would someone please tell me what it is that I am doing wrong. I am sure it is a rather simple to rectify. And if someone knows of any websites that have good tutorials for Python please email me with the addresses. A big thankyou in advance to anyone that can help. Regards, ----------------------------------------------------------------- Vaughan Egan --- celtic(a)ix.net.au ----------------------------------------------------------------- #! python print "Hello World!\n" print "~~~~~~~~~~~~\n" print "and welcome to Python Programming" number = input("Enter a number? ") print "Your number was: ",number userName = input("What is your name? ") print "Hello ",userName

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Editors with Python or Active Scripting capability?
by Peter Hansen Sept. 3, 2000

Sept. 3, 2000

I've become rather intent on *not* using languages other than Python extreme in cases of extreme need. This stems directly from the fact that it works in so many different areas, and vastly increases our productivity. [Embedded stuff (at least on 16-bit micros with 1K of RAM) qualifies as extreme need, as does working with legacy code written in less desirable languages, but most of our work suits Python well.] Writing scripts for a text editor, however, does not qualify as an area where I'm willing to waste time learning or using a language which some shortsighted company or programmer decided *I* should learn just to use its/his/her product. Unfortunately, it seems my choices are fairly limited. I'm frankly surprised by this, given that (no death threats, please!) I do most of my development on (not for!) Windows 98 boxes, where Microsoft has done at least one thing right in the last decade in opening up scripting to non-Microsoft languages via the Active Scripting Host API. In spite of that, the list of text editors supporting Python scripting seems fairly pathetic. So far as I can tell, I'm limited to something called Zeus (which reduced my computer speed to about 23 Hz while running my script), VIM (modes? just say "no"!), and CRedit (which is the only editor I've seen claiming ASH support) which unfortunately says that out of all the possible Active Scripting languages, for some reason Python is the only one which doesn't work! http://www.zeusedit.com/ http://www.vim.org/ http://www.geocities.com/plamen_p/credit/index.html My question is, does anybody know of a decent text editor which uses Python, either "natively" or via Active Scripting, as a scripting/macro language? Thank you for any suggestions you have. ------------------------------------------- Peter Hansen

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Where is BoBo?
by Franz GEIGER Sept. 3, 2000

Sept. 3, 2000

I wondered what's all about Bobo but could not find it: The link www.digicool.com/releases/bobo/ everyone refers to is broken. Any hints? Thanks in advance Franz GEIGER

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Python and interfaces/abstract classes
by Vincent Joseph Sept. 3, 2000

Sept. 3, 2000

Hi, The python faq [6.21] indicates that this feature is not supported, but that enforcement can be checked with a good test module. While certainly possible, this approach may not be practical in all situations. Does anyone know if support for interfaces will be provided in future versions of python ? Thanks in advance, Vincent

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SlickEdit Users......Python setup...
by Amir Mistric Sept. 2, 2000

Sept. 2, 2000

Can someone who uses Visual Slick Edit post config file for Python ??? Thanks Amir

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Guido van Rossum supports simple print. (1991)
by thor＠localhost.localdomain Sept. 2, 2000

Sept. 2, 2000

Guido vs Guido No comments, just the plain reasons: Subject: Why print is a built-in statement From: Guido van Rossum guido@c... X-Organization: CWI, Kruislaan 413, 1098 SJ Amsterdam, The Netherlands X-Phone: +31 20 5924127 (work), +31 20 6225521 (home), +31 20 5924199 (fax) Date: Sat, 07 Dec 91 15:00:00 +0100 -------- Steven Majewski mentioned one issue that I didn't address yet: why "print" is built-in in Python. I'd like to explain this. One of the reasons is that a simple print statement is useful for simple programs. Being a statement it doesn't need parentheses around its argument list, which saves some typing. Another reason is that it treats arguments separated by commas differently than a single argument consisting of a tuple: print 'x =', x might print x = 3.14 while t = 'x =', x print t would print ('x =', 3.14) (This has to do with the function argument discussion, by the way.) The third reason has to do with the final linefeed written by print: again, for simple programs, it's desirable that the simplest form of print statement prints a complete line; but there also must be a way to print partial lines. Using special syntax (a trailing comma) to specify the alternate behavior seemed preferable over having two functions like Pascal's write and writeln (especially since it would have meant two reserved words given the choice for non-function syntax). Writing it down makes it all sound like feeble excuses for a real solution; but everything else I could think of had other disadvantages. Perhaps printing is one of these things that are important enough to warrant more than one way to do things, even in Python... --Guido van Rossum, CWI, Amsterdam guido@c... "*Nobody* expects the Spanish Inquisition" Well, I'm Spanish... :P --- MGA

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[FAQTS] Python Knowledge Base Update -- September 2nd, 2000
by Fiona Czuczman Sept. 2, 2000

Sept. 2, 2000

Hi Guys, The latest entries into http://python.faqts.com regards, Fiona ## Unanswered Questions ######################################## ------------------------------------------------------------- How to limit the max number of simultaneous conections in a server implemented with asyncore.py http://www.faqts.com/knowledge-base/view.phtml/aid/5681 ------------------------------------------------------------- Eduardo Roldan ## New Entries ################################################# ------------------------------------------------------------- Is it possible to determine the name of the currently executing function? http://www.faqts.com/knowledge-base/view.phtml/aid/5702 ------------------------------------------------------------- Fiona Czuczman Alex Martelli Sure -- piece o' cake...: def caller(n=1): from traceback import extract_stack stack = extract_stack() return stack[-n-2][2] # Example usage: def a(): print "this is", caller(0) b() def b(): print "and this is",caller(0), print "called by",caller() Expected output by calling a(): this is a and this is b called by a ------------------------------------------------------------- What is File-like Object? http://www.faqts.com/knowledge-base/view.phtml/aid/5703 ------------------------------------------------------------- Fiona Czuczman Pete Shinners, Will Ware a file-like object is any object (including the regular file object) that has the same methods as the file object. this would typically be the .read() and/or .write() methods. The reason many modules mention they take a file-like object is to give the developer more flexibility. Instead of only taking a file object, they can take any python object with the same set of methods. Most of the time you will probably just use a regular file object. but you can also use many other objects if you want. usual suspects would be stuff like sys.stdout, stringio, and similar things (actually, sys.stdout really is a file object) hopefully that's not too confusing. if you're still not sure, just use a regular file object and don't sweat it. (not sure as to your newbie-ness, a file object is returned from the open() command) :] ------------------ It's an object that behaves like a file. That is to say, it implements the methods a file would normally have, such as read(), readline(), readlines(), write(), flush(), and so forth. You can find out more about files and their methods in the Python Tutorial at http://www.python.org/doc/current/tut/tut.html The part about files is section 7.2. ------------------------------------------------------------- Can I implement access control in my classes (equivalent to C++'s private, public, protected, etc...)? http://www.faqts.com/knowledge-base/view.phtml/aid/5705 ------------------------------------------------------------- Fiona Czuczman Alex Martelli Naming an item with two leading underscores (and without two _trailing_ underscores as well) is as close to "private" as Python comes (the compiler decorates the attribute name with the classname, so no accidental clash is possible any more). There is, AFAIK, no parallel to "protected" (nor any particular need for it; it is, after all, a feature which Stroustrup deeply regrets having let himself be talked intro introducing in C++ -- see his excellent book "Design & Evolution of the C++ Programming Language"). ------------------------------------------------------------- Is there a python script similar to shelve or pickle that will take an array and convert it to XML code? http://www.faqts.com/knowledge-base/view.phtml/aid/5706 ------------------------------------------------------------- Fiona Czuczman Michal Wallace Problem: We have several arrays, some are multidimensional arrays, created with NumPy. We'd like store these arrays in an XML data structure. Is there a python script similar to shelve or pickle that will take an array and convert it to XML code? Thanks. Solution: The xmlrpc module has routines to convert structures to XML (it's on www.pythonware.com) .. But if you want more control over what the XML looks like, you could always start with something like: def xmlify(somearray): res = "<cell>" for item in somearray: if type(item)==type([]): res = res + xmlify(item) else: res = res + item res = res + "</cell>" return res print '<?xml version="1.0"?>' print xmlify(yourMultiDimensionalArray) ------------------------------------------------------------- How can I get a file's permissions? http://www.faqts.com/knowledge-base/view.phtml/aid/5707 ------------------------------------------------------------- Fiona Czuczman Fredrik Lundh Problem: I have been able to get a file's owner and group IDs using the os.stat function but it doesn't seem to give me the file's permissions. Solution: the first member of the stat tuple (ST_MODE) contains the permissions, as a bitmask. you can use the functions and macros in the "stat" module to decipher them. st = os.stat(myfile) mode = st[stat.ST_MODE] if mode & stat.ST_IREAD: print "readable" if mode & stat.ST_IWRITE: print "writable" if mode & stat.ST_IEXEC: print "executable" Problem cont.: Thanks for your help but I only seem to be able to check whether or not the user running the script has "rwx" permissions. I am looking to find the permissions for owner/group/other, preferably in numeric mode. Solution: did you try printing the "mode" value? I'm pretty sure it does contain the "numeric mode" you're looking for. try this: st = os.stat(myfile) mode = st[stat.ST_MODE] print "mode is", octal(mode & 0777) (looking in the stat module source file may also help; it's in Python's Lib directory) ------------------------------------------------------------- Is there a simple way of displaying an error message dialog box in Tkinter? http://www.faqts.com/knowledge-base/view.phtml/aid/5708 ------------------------------------------------------------- Fiona Czuczman Yaniv, Fredrik Lundh Of-course there is: from tkMessageBox import * showerror(<title>, <message>) ----------- check out the tkMessageBox module, documented here: http://w1.132.telia.com/~u13208596/tkintrobook/standard-dialogs.htm ------------------------------------------------------------- How do I do do simple interpolation using NumPy? http://www.faqts.com/knowledge-base/view.phtml/aid/5709 ------------------------------------------------------------- Fiona Czuczman Nick Bower import arrayfns new_y = arrayfns.interp(y,x,new_x) ## Edited Entries ############################################## ------------------------------------------------------------- How to "expire" a web page with Python ? http://www.faqts.com/knowledge-base/view.phtml/aid/5664 ------------------------------------------------------------- Quynh Nguyen Anh, Fiona Czuczman Calvelo Daniel Not sure whether I understand the question, but it looks as if you want to print """<meta http-equiv="expires" content="some_date">""" at the beginning (within the <head>er) of the script generating a page. Still not sure I understand the question and/or/if it is a Python question... HTH anyway.

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Sockets tutorial more in depth than the HOWTO
by Ron Johnson, Jr. Sept. 2, 2000

Sept. 2, 2000

Hello, Having read http://www.python.org/doc/howto/sockets/sockets.html I was wondering if there are any more comprehensive tutorials on the web, even if they are C-based. Sincerely, Ron -- 123456789012345678901234567890123456789012345678901234567890 +----------------------------------------------------------+ | Ron Johnson, Jr. Home: ronjohn(a)gs.verio.net | | Jefferson, LA USA WWW : ronjohnsonjr(a)yahoo.com | | | | Most overused words: feel, cool/kewl, fun, myBlah.com | | Most underused word: think | +----------------------------------------------------------+

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Calling Ada from Python
by hoffman＠insync.net Sept. 2, 2000

Sept. 2, 2000

Hi, I would like to be able to call Ada from Python, so I created a simple example of a Python module written in C which in turn calls functions written in Ada. It works, but one thing is a bit awkward and I am hoping that someone here can help me to improve it. I have attached the C source file that creates the Python module as listing one, and the Ada package (specification and body) that it calls as listing two. For good measure, listing three shows how I built all of this under Linux. The awkwardness comes from the lines (marked AWKWARD in the C source code) that start and stop the Ada runtime library. It is awkward because I start and stop it for each function call. Now, I know that I could turn off the Ada runtime without giving up anything significant as far as this simple example is concerned (though any pointers about how to do this or comments about what capabilities I sacrifice will be appreciated). But I am wondering if Python would allow a better solution. To create a Python extension in C, a module initialization function must be provided (in this case it is called initnumberPlay()). It is clear to me that the call to adainit(), which starts the Ada runtime, could easily be put into this function so that the Ada runtime would be started when the module is loaded. But how can I ensure that the Ada runtime is shutdown when the module exits? I haven't found anything in my reading that suggests a method of cleaning up when a module is unloaded. I do recall reading that the Python interpreter unloads modules before shutting down, so all that I would need to worry about is triggering a call to adafinal() when the module numberPlay is unloaded. If anyone has any suggestions on how to do this, or any other suggestions for improving this code, please let me know. David Hoffman hoffman(a)insync.net =============================<LISTING ONE>============================== /********************************************************************* * * * File: numberPlay.c * * * * Purpose: To provide a demonstration of how to write a C wrapper * * for Ada functions called from Python. * * * * Author: David Hoffman * * hoffman(a)insync.net * * * *********************************************************************/ #include <Python.h> /* Declare external functions....................................... */ extern adainit(); extern adafinal(); extern long adafactorial(long N); extern long adagcd(long P, long Q); /* C functions used to extend Python................................. */ long factorial (long value) /* Compute factorial */ { long answer; adainit(); /* AWKWARD */ answer = adafactorial(value); adafinal(); /* AWKWARD */ return answer; } long gcd (long x, long y) /* Compute greatest common divisor */ { long answer; adainit(); /* AWKWARD */ answer = adagcd(x,y); adafinal(); /* AWKWARD */ return answer; } /* C wrapper functions for Python extensions......................... */ PyObject *wrap_factorial(PyObject *self, PyObject *args) { int n, result; if (!PyArg_ParseTuple(args,"i",&n)) return NULL; if ( n > 0 ) /* Input error check */ { if ( n <= 12 ) { result = factorial(n); } else { PyErr_SetString(PyExc_ValueError,"Input would cause overflow"); return NULL; } } else { PyErr_SetString(PyExc_ValueError,"Input must be non-negative"); return NULL; } return Py_BuildValue("i",result); } PyObject *wrap_gcd(PyObject *self, PyObject *args) { int p, q, result; if (!PyArg_ParseTuple(args,"ii",&p,&q)) return NULL; if ( p <= 0 || q <= 0 ) /* Input error check */ { PyErr_SetString(PyExc_ValueError,"Both inputs must be positive"); return NULL; } else { result = gcd(p,q); } return Py_BuildValue("i",result); } /* Define methods table.............................................. */ static PyMethodDef numberPlayMethods[] = { { "factorial" , wrap_factorial , 1 }, { "gcd" , wrap_gcd , 1 }, { NULL , NULL }, }; /* Initialization function........................................... */ void initnumberPlay() { PyObject *m; m = Py_InitModule("numberPlay", numberPlayMethods); } =============================<LISTING TWO>============================== ------------------------------------------------------------------------ -- -- -- File: integer_functions.ads -- -- -- -- Purpose: To demonstrate how to export Ada functions to C with -- -- the ultimate goal of making them callable from Python -- -- scripts. -- -- -- -- Author: David Hoffman -- -- hoffman(a)insync.net -- -- -- ------------------------------------------------------------------------ with Interfaces.C; use Interfaces; package Integer_Functions is function Ada_Factorial ( Value : C.Long ) return C.Long; function Ada_GCD ( Dividend, Divisor : C.Long ) return C.Long; pragma Export (C, Ada_Factorial, "adafactorial"); pragma Export (C, Ada_GCD, "adagcd"); end Integer_Functions; ------------------------------------------------------------------------ -- -- -- File: integer_functions.adb -- -- -- -- Purpose: To compute either the factorial of a given integer or -- -- the greatest common divisor of a pair of integers with -- -- Ada code invoked from a Python script. -- -- -- -- Author: David Hoffman -- -- hoffman(a)insync.net -- -- -- ------------------------------------------------------------------------ with Interfaces.C; use Interfaces; package body Integer_Functions is ------------------------------------------------------------------------ -- P R I V A T E F U N C T I O N S -- ------------------------------------------------------------------------ -- -- In a "real world" application, the functions in this section -- would be defined and implemented in an external package that -- would be linked to this one via with and use statements. -- -- Compute factorial.................................................... function Factorial ( N : Integer ) return Integer is begin if N = 1 then return 1; else return N * Factorial(N-1); end if; end; -- Compute greatest common divisor...................................... function GCD ( I, J : Natural ) return Natural is begin if J = 0 then return I; else return GCD(J, I mod J ); end if; end; ------------------------------------------------------------------------ -- P U B L I C F U N C T I O N S -- ------------------------------------------------------------------------ -- Export factorial..................................................... function Ada_Factorial ( Value : C.Long ) return C.Long is P, Q : Integer; begin P := Integer(Value); Q := Factorial(P); return C.Long(Q); end; -- Export greatest common divisor....................................... function Ada_GCD ( Dividend, Divisor : C.Long ) return C.Long is N, P, Q : Natural; begin N := Natural(Dividend); P := Natural(Divisor); Q := GCD(N,P); return C.Long(Q); end; end Integer_Functions; ============================<LISTING THREE>============================= This example was built under Linux (kernel 2.0.33, libc 5.4.33) using the GNAT Ada compiler (version 3.11p). It runs under Python 1.5. The first step is to compile the Ada components: $ gcc -c integer_functions.ads $ gcc -c integer_functions.adb $ gnatbind -n integer_functions.ali $ gcc -c b_integer_functions.c Then compile the C component: $ gcc -fpic -c -I/usr/local/include/python1.5 \ -I/usr/local/lib/python1.5/config \ numberPlay.c Finally, link it all together: $ gcc -shared -o numberPlay.so \ -L/usr/lib/gcc-lib/i686-pc-linux-gnulibc1/2.8.1/adalib \ *.o -lgnat Good luck. ========================================================================

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