Develop Reference

Unicode issues with tarfile.extractall() (Python 2.7)

I'm using python 2.7.6 on Windows and I'm using the tarfile module to extract a file a gzip file. The mode option of tarfile.open() is set to "r:gz". After the open call, if I were to print the contents of the archive via tarfile.list(), I see the following directory in the list:
./静态分析 Part 1.v1/
However, after I call tarfile.extractall(), I don't see the above directory in the extracted list of files, instead I see this:
é™æ€åˆ†æž Part 1.v1/
If I were to extract the archive via 7zip, I see a directory with the same name as the first item above. So, clearly, the extractall() method is screwing up, but I don't know how to fix this.

I learned that tar doesn't retain the encoding information as part of the archive and treats filenames as raw byte sequences. So, the output I saw from tarfile.extractall() was simply raw the character sequence that comprised the file's name prior to compression. In order to get the extractall() method to recreate the original filenames, I discovered that you have to manually convert the members of the TarFile object to the appropriate encoding before calling extractall(). In my case, the following did the trick:
modeltar = tarfile.open(zippath, mode="r:gz")
updatedMembers = []
for m in modeltar.getmembers():
m.name = unicode(m.name, 'utf-8')
updatedMembers.append(m)
modeltar.extractall(members=updatedMembers, path=dbpath)
The above code is based on this superuser answer: https://superuser.com/a/190786/354642

Python: How to get the URL to a file when the file is received from a pipe?

I created, in Python, an executable whose input is the URL to a file and whose output is the file, e.g.,
file:///C:/example/folder/test.txt --> url2file --> the file
Actually, the URL is stored in a file (url.txt) and I run it from a DOS command line using a pipe:
type url.txt | url2file
That works great.
I want to create, in Python, an executable whose input is a file and whose output is the URL to the file, e.g.,
a file --> file2url --> URL
Again, I am using DOS and connecting executables via pipes:
type url.txt | url2file | file2url
Question: file2url is receiving a file. How do I get the file's URL (or path)?

In general, you probably can't.
If the url is not stored in the file, I seems very difficult to get the url. Imagine someone reads a text to you. Without further information you have no way to know what book it comes from.
However there are certain usecases where you can do it.
Pipe the url together with the file.
If you need the url and you can do that, try to keep the url together with the file. Make url2file pipe your url first and then the file.
Restructure your pipeline
Maybe you don't need to find the url for the file, if you restructure your pipeline.
Index your files
If only a certain files could potentially be piped into file2url, you could precalculate a hash for all files and store it in your program together with the url. In python you would do this using a dict where the key is the file (as a string) and the value is the url. You could use pickle to write the dict object to a file and load it at the start of your program.
Then you could simply lookup the url from this dict.
You might want to research how databases or search functions in explorers handle indexing or alternative solutions.
Searching for the file
You could use one significant line of the file and use something like grep or head on linux to search all files of your computer for this line. Note that grep and head are programs, not python functions. For DOS, you might need to google the equivalent programs.
FYI: grep searches for one line of text inside a file.
head puts out the first few lines of a file. I suggest comparing only the first few lines of files to avoid searching through huge file.
Searching all files on the computer might take very long.
You could only search files with the same size as your piped input.
Use url.txt
If file2url knows the location of the file url.txt, then you could look up all files in url.txt until you find a file identical to the file that was piped into your program. You could combine this with the hashing/ indexing solution.

'file2url' receives the data via standard input (like keyboard).
The data is transferred by the kernel and it doesn't necessarily have to have any file-system representation. So if there's no file there's no URL or path to that for you to get.

Let's try to do it by obvious way:
$ cat test.py | python test.py
import sys
print ''.join(sys.stdin.readlines())
print sys.stdin.name
<stdin>
So, filename is "< stdin>" because, for the python there is no filename - only input.
Another way is a system-dependent. Find a command line, which was used, for example, but no garantee that is will be works.

How to write input files with comments in Python

I need to write some input data files for a python program, and I need the full thing:
comments, spacing, variable = value, etc.
Is there any library (line argparser for command line arguments) for python or should I write my own?
Thanks!

Take a look at the ConfigParser module (renamed to configparser in Python 3).
Alternatively, you could simply write the input data using Python syntax, and import the result into your main program.

Does the syntax have to look like that? Could you just use a character delimited file (like csv or tab-delimited) with each predefined field in a separate column? Python has well defined modules to handle csv data.
If you specifically want input files that present blocks of code, then aix's suggestion of importing would also work.

Python parsing xml directly from web address

Hey. I tried to find a way but i can't. I have set up a xml.sax parser in python and it works perfect when i read a local file (for example calendar.xml), but i need to read a xml file from a web address.
I figured it would work if i do this:
toursxml='http://api.songkick.com/api/3.0/artists/mbid:'+mbid+'/calendar.xml?apikey=---------'
toursurl=urllib2.urlopen(toursxml)
toursurl=toursurl.read()
parser.parse(toursurl)
but it doesnt. im sure theres an easy way but i cant find it.
so yeah I can easily go to the url and download the file and open it by doing
parser.parse("calendar.xml")
as a work around ive set it up to read the file and create the file locally, close the file, and then read it. But as you can guess its slow as hell.
Is there anyone to directly read the xml? also note that the url name does not end in ".xml" so that may be a problem later

First, your example is mixed up. Please don't reuse variables.
toursurl= urllib2.urlopen(toursxml)
toursurl_string= toursurl.read()
parser.parseString( toursurl_string )
Reads the entire file into a string, named toursurl_string.
To parse a string, you use the parseString(toursurl_string) method.
http://docs.python.org/library/xml.sax.html#xml.sax.parseString
If you want to combine reading and parsing, you have to pass the "stream" or filename to parse.
toursurl= urllib2.urlopen(toursxml)
parser.parse(toursurl)

parser.parse(xyz)
expects xyz to be a file; you are looking for
parser.parseString(xyz)
which expects xyz to be a string containing XML.

How to separate content from a file that is a container for binary and other forms of content

I am trying to parse some .txt files. These files serve as containers for a variable number of 'children' files that are set off or identified within the container with SGML tags. With python I can easily separate the children files. However I am having trouble writing the binary content back out as a binary file (say a gif or jpg). In the simplest case the container might have an embedded html file followed by a graphic that is called by the html. I am assuming that my problem is because I am reading the original .txt file using open(filename,'r'). But that seems the only option to find the sgml tags to split the file.
I would appreciate any help to identify some relevant reading material.
I appreciate the suggestions but I am still struggling with the most basic questions. For example when I open the file with wordpad and scroll down to the section tagged as a gif I see this:
<FILENAME>h65803h6580301.gif
<DESCRIPTION>GRAPHIC
<TEXT>
begin 644 h65803h6580301.gif
M1TE&.#EA(P)I`=4#`("`#,#`P$!`0+^_OW]_?_#P\*"#H.##X-#0T&!#8!`0
M$+"PL"`#('!P<)"0D#`P,%!04#\_/^_O[Y^?GZ^OK]_?WX^/C\_/SV]O;U]?
I can handle finding the section easily enough but where does the gif file begin. Does the header start with 644, the blanks after the word begin or the line beginning with MITE?
Next, when the file is read into python does it do anything to the binary code that has to be undone when it is read back out?
I can find the lines where the graphics begin:
filerefbin=file('myfile.txt','rb')
wholeFile=filerefbin.read()
import re
graphicReg=re.compile('<DESCRIPTION>GRAPHIC')
locationGraphics=graphicReg.finditer(wholeFile)
graphicsTags=[]
for match in locationGraphics:
graphicsTags.append(match.span())
I can easily use the same process to get to the word begin, or to identify the filename and get to the end of the filename in the 'first' line. I have also successefully gotten to the end of the embedded gif file. But I can't seem to write out the correct combination of things so when I double click on h65803h6580301.gif when it has been isolated and saved I get to see the graphic.
Interestingly, when I open the file in rb, the line endings appear to still be present even though they don't seem to have any effect in notebpad. So that is clearly one of my problems I might need to readlines and join the lines together after stripping out the \n
I love this site and I love PYTHON
This was too easy once I read bendin's post. I just had to snip the section that began with the word begin and save that in a txt file and then run the following command:
import uu
uu.decode(r'c:\test2.txt',r'c:\test.gif')
I have to work with some other stuff for the rest of the day but I will post more here as I look at this more closely. The first thing I need to discover is how to use something other than a file, that is since I read the whole .txt file into memory and clipped out the section that has the image I need to work with the clipped section instead of writing it out to test2.txt. I am sure that can be done its just figuring out how to do it.

What you're looking at isn't "binary", it's uuencoded. Python's standard library includes the module uu, to handle uuencoded data.
The module uu requires the use of temporary files for encoding and decoding. You can accomplish this without resorting to temporary files by using Python's codecs module like this:
import codecs
data = "Let's just pretend that this is binary data, ok?"
uuencode = codecs.getencoder("uu")
data_uu, n = uuencode(data)
uudecode = codecs.getdecoder("uu")
decoded, m = uudecode(data_uu)
print """* The initial input:
%(data)s
* Encoding these %(n)d bytes produces:
%(data_uu)s
* When we decode these %(m)d bytes, we get the original data back:
%(decoded)s""" % globals()

You definitely need to be reading in binary mode if the content includes JPEG images.
As well, Python includes an SGML parser, http://docs.python.org/library/sgmllib.html .
There is no example there, but all you need to do is setup do_ methods to handle the sgml tags you wish.

You need to open(filename,'rb') to open the file in binary mode. Be aware that this will cause python to give You confusing, two-byte line endings on some operating systems.