🌐 Mailman 3 December 2004 - Python-list - python.org

Is it possible to open a dbf
by John Fabiani Jan. 4, 2005

Jan. 4, 2005

Hi, I'm wondering if there is a module available that will open a dbf (actually sco foxpro 2.6) file under linux. Hopefully it will be DAPI 2.0 but I'll accept anything at this point. John

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what is lambda used for in real code?
by Steven Bethard Jan. 3, 2005

Jan. 3, 2005

I thought it might be useful to put the recent lambda threads into perspective a bit. I was wondering what lambda gets used for in "real" code, so I grepped my Python Lib directory. Here are some of the ones I looked, classified by how I would rewrite them (if I could): * Rewritable as def statements (<name> = lambda <args>: <expr> usage) These are lambdas used when a lambda wasn't needed -- an anonymous function was created with lambda and then immediately bound to a name. Since this is essentially what def does, using lambdas here is (IMHO) silly. pickletools.py: getpos = lambda: None def getpos(): return None tarfile.py: normpath = lambda path: os.path.normpath(path).replace(os.sep, "/") def normpath(path): os.path.normpath(path).replace(os.sep, "/") urllib2.py: H = lambda x: md5.new(x).hexdigest() def H(x): md5.new(x).hexdigest() urllib2.py: H = lambda x: sha.new(x).hexdigest() def H(x): sha.new(x).hexdigest() * Rewritable with existing functions Mainly these are examples of code that can benefit from using the functions available in the operator module, especially operator.itemgetter and operator.attrgetter (available in 2.4) cgi.py: return map(lambda v: v.value, value) return map(operator.attrgetter('value'), value) CGIHTTPServer.py: nobody = 1 + max(map(lambda x: x[2], pwd.getpwall())) nobody = 1 + max(map(operator.itemgetter(2), pwd.getpwall())) SimpleXMLRPCServer.py: server.register_function(lambda x,y: x+y, 'add') server.register_function(operator.add, 'add') SimpleXMLRPCServer.py: server.register_function(lambda x,y: x+y, 'add') server.register_function(operator.add, 'add') sre_constants.py: items.sort(key=lambda a: a[1]) items.sort(key=operator.itemgetter(1)) tarfile.py: return map(lambda m: m.name, self.infolist()) return map(operator.attrgetter('name'), self.infolist()) * Rewritable with list comprehensions/generator expressions Lambdas in map or filter expressions can often be replaced by an appropriate list comprehension or generator expression (in Python 2.3/2.4) cgi.py: plist = map(lambda x: x.strip(), line.split(';')) plist = [x.strip() for x in line.split(';') cgi.py: return map(lambda v: v.value, value) return [v.value for v in value] CGIHTTPServer.py: nobody = 1 + max(map(lambda x: x[2], pwd.getpwall())) nobody = 1 + max(x[2] for x in pwd.getpwall()) glob.py: names=filter(lambda x: x[0]!='.',names) names=[x for x in names if x[0] != '.'] hmac.py: return "".join(map(lambda x, y: chr(ord(x) ^ ord(y)), s1, s2)) return "".join(chr(ord(x) ^ ord(y)) for x, y in zip(s1, s2)) imaplib.py: l = map(lambda x:'%s: "%s"' % (x[0], x[1][0] and '" "'.join(x[1]) or ''), l) l = ['%s: "%s"' % (x[0], x[1][0] and '" "'.join(x[1]) or '') for x in l] inspect.py: suffixes = map(lambda (suffix, mode, mtype): (-len(suffix), suffix, mode, mtype), imp.get_suffixes()) suffixes = [(-len(suffix), suffix, mode, mtype) for suffix, mode, mtype in imp.get_suffixes() inspect.py: return join(map(lambda o, c=convert, j=join: strseq(o, c, j), object)) return join([strseq(o, convert, join) for o in object]) mailcap.py: entries = filter(lambda e,key=key: key in e, entries) entries = [e for e in entries if key in e] poplib.py: digest = ''.join(map(lambda x:'%02x'%ord(x), digest)) digest = ''.join('%02x' % ord(x) for x in digest) pstats.py: if line and not filter(lambda x,a=abbrevs: x not in a,line.split()): if line and not [x for x in line.split() if x not in abbrevs]: tabnanny.py: firsts = map(lambda tup: str(tup[0]), w) firsts = [str(tup[0]) for tup in w] tarfile.py: return map(lambda m: m.name, self.infolist()) return [m.name for m in self.infolist()] tarfile.py: return filter(lambda m: m.type in REGULAR_TYPES, self.tarfile.getmembers()) return [m for m in self.tarfile.getmembers() if m.type in REGULAR_TYPES] urllib2.py: return map(lambda x: x.strip(), list) return [x.strip() for x in list] webbrowser.py: _tryorder = filter(lambda x: x.lower() in _browsers or x.find("%s") > -1, _tryorder _tryorder = [x for x in _tryorder if x.lower() in _browsers or x.find("%s") > -1] * Functions I don't know how to rewrite Some functions I looked at, I couldn't figure out a way to rewrite them without introducing a new name or adding new statements. (Warning: I have trouble following code that uses 'reduce', so I only glossed over lambdas in reduce calls.) calendar.py: _months.insert(0, lambda x: "") cgitb.py: inspect.formatargvalues(args, varargs, varkw, locals, formatvalue=lambda value: '=' + pydoc.html.repr(value)) cgitb.py: inspect.formatargvalues(args, varargs, varkw, locals, formatvalue=lambda value: '=' + pydoc.text.repr(value)) csv.py: quotechar = reduce(lambda a, b, quotes = quotes: (quotes[a] > quotes[b]) and a or b, quotes.keys()) csv.py: delim = reduce(lambda a, b, delims = delims: (delims[a] > delims[b]) and a or b, delims.keys()) difflib.py: matches = reduce(lambda sum, triple: sum + triple[-1], self.get_matching_blocks(), 0) gettext.py: return eval('lambda n: int(%s)' % plural) gettext.py: self.plural = lambda n: int(n != 1) inspect.py: classes.sort(key=lambda c: (c.__module__, c.__name__)) inspect.py: def formatargspec(args, varargs=None, varkw=None, ... formatvarargs=lambda name: '*' + name, formatvarkw=lambda name: '**' + name, formatvalue=lambda value: '=' + repr(value), inspect.py: def formatargvalues(args, varargs, varkw, locals, ... formatvarargs=lambda name: '*' + name, formatvarkw=lambda name: '**' + name, formatvalue=lambda value: '=' + repr(value), pyclbr.py: objs.sort(lambda a, b: cmp(getattr(a, 'lineno', 0), getattr(b, 'lineno', 0))) SimpleHTTPServer.py: list.sort(key=lambda a: a.lower()) subprocess.py: p = Popen(["id"], preexec_fn=lambda: os.setuid(100)) symtable.py: self.__params = self.__idents_matching(lambda x: x & DEF_PARAM) symtable.py: self.__locals = self.__idents_matching(lambda x: x & DEF_BOUND) symtable.py: self.__globals = self.__idents_matching(lambda x: x & glob) urllib2.py:setattr(self, '%s_open' % type, lambda r, proxy=url, type=type, meth=self.proxy_open: meth(r, proxy, type)) xdrlib.py: unpacktest = [ (up.unpack_uint, (), lambda x: x == 9), (up.unpack_bool, (), lambda x: not x), (up.unpack_bool, (), lambda x: x), (up.unpack_uhyper, (), lambda x: x == 45L), (up.unpack_float, (), lambda x: 1.89 < x < 1.91), (up.unpack_double, (), lambda x: 1.89 < x < 1.91), (up.unpack_string, (), lambda x: x == 'hello world'), (up.unpack_list, (up.unpack_uint,), lambda x: x == range(5)), (up.unpack_array, (up.unpack_string,), lambda x: x == ['what', 'is', 'hapnin', 'doctor']), ] Of the functions that I don't know how to rewrite, I think there are a few interesting cases: (1) lambda x: "" This is the kind of parameter adaptation that I think Jeff Shannon was talking about in another lambda thread. Using the ignoreargs function I suggested there[1], you could rewrite this as: ignoreargs(str, 1) (2) lambda a: a.lower() My first thought here was to use str.lower instead of the lambda, but of course that doesn't work if 'a' is a unicode object: py> str.lower(u'a') Traceback (most recent call last): File "<interactive input>", line 1, in ? TypeError: descriptor 'lower' requires a 'str' object but received a 'unicode' It's too bad I can't do something like: basestring.lower (3) self.plural = lambda n: int(n != 1) Note that this is *almost* writable with def syntax. If only we could do: def self.plural(n): int(n != 1) (4) objs.sort(lambda a, b: cmp(getattr(a, 'lineno', 0), getattr(b, 'lineno', 0))) My first intuition here was to try something like: objs.sort(key=operator.attrgetter('lineno')) but this doesn't work because then we don't get the default value of 0 if the attribute doesn't exist. I wonder if operator.attrgetter should take an optional "default" parameter like getattr does: Help on built-in function getattr in module __builtin__: getattr(...) getattr(object, name[, default]) -> value (5) lambda x: x & DEF_PARAM This could probably be written as: functional.partial(operator.and_, DEF_PARAM) if PEP 309[2] was accepted, thought I'm not claiming that's any clearer... So, those are my thoughts on how lambdas are "really" used. If others out there have real-life code that uses lambdas in interesting ways, feel free to share them here! Steve [1]http://mail.python.org/pipermail/python-list/2004-December/257982.html [2]http://python.fyxm.net/peps/pep-0309.html

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Is Python good for graphics?
by Esmail Bonakdarian Jan. 3, 2005

Jan. 3, 2005

First of all, I *really* like Python ;-) I need some help with the graphical side of things. I would like to do some basic graphics with Python, but I am not sure what the best/most effective way for me to do what I want. Basically, I would like to be able to create some basic animations where I can help visualize various sorting algorithms (for instance http://ciips.ee.uwa.edu.au/~morris/Year2/PLDS210/sorting.html#insert_anim) or graph searches (coloring nodes as each gets visited). (Something like this: http://cs.smith.edu/~thiebaut/java/graph/Welcome.html) Or to create and manipulate programmatically a simple 2-D block puzzle (like this: http://www.johnrausch.com/SlidingBlockPuzzles/quzzle.htm). Note, the ability to do this via the web would be nice, but definitely is *not* required at the moment. These would be used to help in learning/teaching. I am aware of Tkinter and wxPython (by aware I mean I know of their existence :-) Before investing (a lot?) of time to learn these, I thought I’d ask the more experienced folks around here what would be the best way to invest my time to get basic graphics going. I really am not concerned so much with efficiency as easy of use. Can anyone recommend what would suit my rather limited needs best? Are there other graphics libraries I should consider that would be more suitable? Or is Python not the way to go for this? Thanks! Esmail

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Tkinter (OOP?) help
by 3c273 Jan. 3, 2005

Jan. 3, 2005

Hello, I am trying to expand on a tutorial I am working through and I am not understanding something. In the following example if you click on the "New window" button, a new window appears with a "Close me" button in it and if you click on it's "Close me" button, it works. But, if you click the original "New window" button two or more times, the "Close me" button only works on one of the new windows. Furthermore, if you click "Close me" on the first new window, it closes the last window to open, not the one that you clicked on. How do I bind a "closeme2" function to each new window? Any help is appreciated. Louis --begin code-- from Tkinter import * class MyApp: def __init__(self, parent): self.myparent = parent self.frame1 = Frame(parent) self.frame1.pack() self.btn1 = Button(self.frame1, text='Do nothing', bg='green') self.btn1.pack(side=LEFT) self.btn2 = Button(self.frame1, text='Close me', fg='white', bg='red') self.btn2.pack(side=LEFT) self.btn2.bind('<Button-1>', self.closeme) self.btn3 = Button(self.frame1, text='New window?', bg='grey') self.btn3.pack(side=LEFT) self.btn3.bind('<Button-1>', self.newwindow) def closeme(self, event): self.myparent.destroy() def newwindow(self, event): self.new = Toplevel(self.myparent) self.frame2 = Frame(self.new) self.frame2.pack() self.btn4 = Button(self.frame2, text='Close me', fg='white', bg='red') self.btn4.pack() self.btn4.bind('<Button-1>', self.closeme2) def closeme2(self, event): self.new.destroy() root = Tk() root.title('Tk Test Program') myapp = MyApp(root) root.mainloop()

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cosmetic Tkinter question
by sean_mcilroy＠yahoo.com Jan. 3, 2005

Jan. 3, 2005

I've got a bunch of Frames, all packed into the root window with side=TOP, and in each Frame I've got a Checkbutton packed with side=LEFT. I expected the Checkbuttons to be flush with the left edge of the window, but they're not, and it looks a little gross. How do I get them to align?

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Re: Switch statement (was: Lambda going out of fashion)
by rzed Jan. 3, 2005

Jan. 3, 2005

Skip Montanaro <skip(a)pobox.com> wrote in news:mailman.8354.1103817745.5135.python-list@python.org: > > Stephen> { > Stephen> 'one': lambda x:x.blat(), > Stephen> 'two': lambda x:x.blah(), > Stephen> }.get(someValue, lambda x:0)(someOtherValue) > > One thing to remember is that function calls in Python are > pretty damn expensive. If x.blat() or x.blah() are themselves > only one or two lines of code, you might find that your "switch" > statement is better written as an if/elif/else statement. > You're making potentially three function calls (get(), lambda > and x.blat() or x.blah()) to perform what might only be a small > handful of inline statements. I'll ignore the readability cost > of your solution vs. an if statement. > > Stephen> So, the questions I am asking are: Is this okay > with everyone? > > Sure. I'll adjust. > > Stephen> Does anyone else feel that lambda is useful in this > kind of Stephen> context? > > It's useful in this sort of context. It will probably always be > limited to single expressions, which will always leave it a > second-class citizen in Python. Interestingly enough, lambda in > the Lisp world has the same limitation, however, since Lisp code > is nothing but a series of s-expressions, that's not a problem. > > Stephen> Are there alternatives I have not considered? > > I've never seen a situation where if/elif/else wasn't adequate > or was less clear than the many attempts at switch-like > behavior. > > Folks (in general), there is still an open PEP on a switch > statement for Python. It's been idle since late 2001: > > http://www.python.org/peps/pep-0275.html > > It would help if interested people were to take a look at it and > identify open issues. If you google for pep 275 you will > probably find relevant python-dev discussions from the 2001/2002 > timeframe. Thomas Wouters' patch for the interpreter would also > need to be resurrected and brought up-to-date. I not longer > remember why the PEP stalled. > It seems to me that it was regarded as misguidod. -- rzed

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File locking is impossible in Windows?
by Pekka Niiranen Jan. 3, 2005

Jan. 3, 2005

Hi, I have used the following example from win32 extensions: -----SCRIPT STARTS---- import win32file import win32con import win32security import pywintypes class Flock: def __init__(self,file): self.file=file secur_att = win32security.SECURITY_ATTRIBUTES() secur_att.Initialize() self.highbits=-0x7fff0000 self.hfile=win32file.CreateFile( self.file,\ win32con.GENERIC_READ|win32con.GENERIC_WRITE,\ win32con.FILE_SHARE_READ|win32con.FILE_SHARE_WRITE,\ secur_att, win32con.OPEN_ALWAYS,\ win32con.FILE_ATTRIBUTE_NORMAL , 0 ) def lock(self): lock_flags=win32con.LOCKFILE_EXCLUSIVE_LOCK|\ win32con.LOCKFILE_FAIL_IMMEDIATELY self.ov=pywintypes.OVERLAPPED() win32file.LockFileEx(self.hfile,lock_flags,0,\ self.highbits,self.ov) def unlock(self): win32file.UnlockFileEx(self.hfile,0,\ self.highbits,self.ov) self.hfile.Close() if __name__ == '__main__': from time import time, strftime, localtime import sys l=Flock("e:\\\\log.txt") print 'calling lock' l.lock() print "Now locked. Hit enter to release lock." dummy = sys.stdin.readline() l.unlock() print 'now unlocked' -----SCRIPT ENDS---- If I start one python process from dos window I get message: E:\>python lockker.py calling lock Now locked. Hit enter to release lock. All well, now if 1) I start another Dos -shell and run the same command I get: E:\>python lockker.py calling lock Traceback (most recent call last): File "lockker.py", line 35, in ? l.lock() File "lockker.py", line 23, in lock win32file.LockFileEx(self.hfile,lock_flags,0,\ self.highbits,self.ov) pywintypes.error: (33, 'LockFileEx',\ 'The process cannot access the file because\ another process has locked a portion of the file.') Which is correct. 2) I try to read the contents of the file from Dos -shell, I get: E:\>type log.txt The process cannot access the file because another\ process has locked a portion of the file. This is correct. 3) When I open the file into notepad.exe I can edit the screen but not write changes to disk. Correct again! 4) I cannot delete the file from Dos shell or from W2K explorer which is correct. 5) However, I can overwrite the file over with: E:\>copy d:\log.txt log.txt 1 file(s) copied. Which is WRONG as is me being able to copy another file over it with W2K explorer too. Is there a way around this? How can I stop file being COPIED OVER while it is being open? Is this window's feature? Is readlines() operation "atomic" enough for me not to worry about these issues? My python script modifies set of files from a directory one by one. I try to lock them all exclusively for the script until all are modified. If one of the files gets overwritten by another version (by another process) the script may fail. -pekka-

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Gate Oxide thickness of CMOS
by hasi＠rediffmail.com Jan. 2, 2005

Jan. 2, 2005

Hi, I would like to know the following details for a CMOS 1.gate oxide thickness 2.The Number of masks 3.Number of transistors per chip Thanks, Hasi!

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when wxPython update to python2.4?
by alang_yl Jan. 2, 2005

Jan. 2, 2005

i can't wait.

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Re: Mailing list hosting?
by jjl＠pobox.com Jan. 2, 2005

Jan. 2, 2005

OK, freelists.org *was* promising. The submit button on the signup page leads to a page displaying raw HTML with no content of interest. I guess the site is no longer active. John

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