Re: [Tutor] checking if data files are good, readable, and exist
"bob gailer" <[EMAIL PROTECTED]> wrote But that isn't. Python just reads the data and interprets it as text if you specify a text file - the default - or as raw data if you use rb. But it DOES handle line-ends in an OS independent manner. OK, I'll grant you that small piece of data manipulation. :-) (Although it could be argued that even that is just translating two bytes into one character in the set.) Alan G. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] checking if data files are good, readable, and exist
Alan Gauld wrote:
But that isn't. Python just reads the data and interprets it
as text if you specify a text file - the default - or as raw data
if you use rb.
But it DOES handle line-ends in an OS independent manner. Windows uses
CR-LF as a line end, whereas Unix, Linux, Mac use (just CR or is it LF?).
Python presents line-ends uniformly as \n when you open the file in text
mode.
Witness: (on Windows)
>>> f = open('c:/foo.txt', 'r')
>>> f.read()
'this line contains as\nbut this has as\n'
>>> f = open('c:/foo.txt', 'rb')
>>> f.read()
'this line contains as\r\nbut this has as\r\n'
[snip]
--
Bob Gailer
919-636-4239 Chapel Hill, NC
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Re: [Tutor] checking if data files are good, readable, and exist
"W W" <[EMAIL PROTECTED]> wrote Am I wrong in thinking that /all/ files are stored as binary? No, thats quite right. python opens them, it automagically opens them in a more readable format, But that isn't. Python just reads the data and interprets it as text if you specify a text file - the default - or as raw data if you use rb. Python doesn't alter the data in any way it simply assumes that its text and interprets the bytes according to the current alphabet. Thus it reads the value 65 and interprets it as 'A' (assuming ASCII) in text mode or just as the bit pattern 0101 in binary. The application must then interpret the bits in whatever way it considers appropriate - ass an integer, a bitmask, part of a graphic image etc. The important point is that there is no distinction between binary data or text data in the file itself its just how it is interpreted that distinguishes them. (This is not completely true on some OS where text files always have an EOF marker, but it is itself just a binary value!) None of which helps the OP other than to highlight the difficulty of determining if a file in binary or not. We can sometimes tell if a file is not text - if it uses ASCII - by looking at the range of byte values, but thats sloowww... but we can never be sure that a file is non text. (We can also check for common file headers such as postscript, GIF, MP3, JPEG, MIDI, etc etc but even they can be misleading if they just coincidentally look valid) HTH, Alan G. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] checking if data files are good, readable, and exist
On Tue, Jul 22, 2008 at 10:40 AM, Bryan Fodness <[EMAIL PROTECTED]> wrote: > I would like to check to see if the data files are good, readable, and > exist. I have checked to see if they exist, but their is a possibility that > the data file might be binary, and I would like to have a sys.exit for that > as well. > > if not os.path.isfile(A_data) or not os.path.isfile(B_data)\ >or not os.path.isfile(C_data) or not os.path.isfile(D_data): > sys.exit(14) > Am I wrong in thinking that /all/ files are stored as binary? And then when python opens them, it automagically opens them in a more readable format, unless you open them in binary with "rb" or similar command? -Wayne -- To be considered stupid and to be told so is more painful than being called gluttonous, mendacious, violent, lascivious, lazy, cowardly: every weakness, every vice, has found its defenders, its rhetoric, its ennoblement and exaltation, but stupidity hasn't. - Primo Levi ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] checking if data files are good, readable, and exist
Bryan Fodness wrote:
I would like to check to see if the data files are good, readable, and
exist. I have checked to see if they exist, but their is a possibility
that the data file might be binary, and I would like to have a sys.exit
for that as well.
You're going to be asked a lot of questions along the lines
of "What do you mean by binary?". I'm going to assume you
mean: has things other than ordinary letters, numbers
and punctuation in it. In today's internationalised and
Unicoded world that's a highly dodgy assumption, but I'm
going to go with it.
To compound the crudeness of my approach, I'm going to
assume that anything > 126 is "binary" (thus dodging
the more complicated issue of the 0-31 control chars).
def is_binary (filename):
return any (ord (c) > 126 for c in open (filename).read ())
print is_binary ("file1.txt")
Obviously, if you know any of the files is going to be
massive, you'll want to do something a bit smarter than
this.
TJG
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[Tutor] checking if data files are good, readable, and exist
I would like to check to see if the data files are good, readable, and exist. I have checked to see if they exist, but their is a possibility that the data file might be binary, and I would like to have a sys.exit for that as well. if not os.path.isfile(A_data) or not os.path.isfile(B_data)\ or not os.path.isfile(C_data) or not os.path.isfile(D_data): sys.exit(14) -- "The game of science can accurately be described as a never-ending insult to human intelligence." - João Magueijo ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
