Mercurial > cpython-lru_cache-weakref

annotate Lib/whichdb.py @ 25838:8540887bcec6 2.2

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Backport of 2.183: Fix memory leak in add_subclass() found by NealN with valgrind.
author Guido van Rossum <guido@python.org>
date Fri, 18 Oct 2002 13:42:21 +0000
parents edd9d0b3c47e
children 062e342ccff5 bcc35a0f1a78
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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c3ec69b1fe36 Function to guess which db package created a database.
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1 """Guess which db package to use to open a db file."""
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2
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3 import os
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4
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5 def whichdb(filename):
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6 """Guess which db package to use to open a db file.
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7
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8 Return values:
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9
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10 - None if the database file can't be read;
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11 - empty string if the file can be read but can't be recognized
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12 - the module name (e.g. "dbm" or "gdbm") if recognized.
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13
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14 Importing the given module may still fail, and opening the
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15 database using that module may still fail.
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16 """
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17
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18 import struct
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19
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20 # Check for dbm first -- this has a .pag and a .dir file
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21 try:
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22 f = open(filename + os.extsep + "pag", "rb")
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23 f.close()
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24 f = open(filename + os.extsep + "dir", "rb")
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25 f.close()
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26 return "dbm"
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27 except IOError:
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28 pass
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29
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30 # Check for dumbdbm next -- this has a .dir and and a .dat file
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31 try:
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32 f = open(filename + os.extsep + "dat", "rb")
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33 f.close()
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34 f = open(filename + os.extsep + "dir", "rb")
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35 try:
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36 if f.read(1) in ["'", '"']:
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37 return "dumbdbm"
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38 finally:
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39 f.close()
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40 except IOError:
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41 pass
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42
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43 # See if the file exists, return None if not
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44 try:
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45 f = open(filename, "rb")
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46 except IOError:
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47 return None
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48
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49 # Read the start of the file -- the magic number
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50 s16 = f.read(16)
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51 f.close()
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52 s = s16[0:4]
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53
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54 # Return "" if not at least 4 bytes
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55 if len(s) != 4:
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56 return ""
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57
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58 # Convert to 4-byte int in native byte order -- return "" if impossible
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59 try:
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60 (magic,) = struct.unpack("=l", s)
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61 except struct.error:
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62 return ""
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63
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64 # Check for GNU dbm
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65 if magic == 0x13579ace:
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66 return "gdbm"
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67
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68 # Check for BSD hash
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69 if magic in (0x00061561, 0x61150600):
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70 return "dbhash"
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71
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72 # BSD hash v2 has a 12-byte NULL pad in front of the file type
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73 try:
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74 (magic,) = struct.unpack("=l", s16[-4:])
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75 except struct.error:
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76 return ""
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77
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78 # Check for BSD hash
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79 if magic in (0x00061561, 0x61150600):
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80 return "dbhash"
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81
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82 # Unknown
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83 return ""