"""Guess which db package to use to open a db file."""

import struct

def whichdb(filename):
    """Guess which db package to use to open a db file.

    Return values:

    - None if the database file can't be read;
    - empty string if the file can be read but can't be recognized
    - the module name (e.g. "dbm" or "gdbm") if recognized.

    Importing the given module may still fail, and opening the
    database using that module may still fail.
    """

    # Check for dbm first -- this has a .pag and a .dir file
    try:
        f = open(filename + ".pag", "rb")
        f.close()
        f = open(filename + ".dir", "rb")
        f.close()
        return "dbm"
    except IOError:
        pass

    # See if the file exists, return None if not
    try:
        f = open(filename, "rb")
    except IOError:
        return None

    # Read the first 4 bytes of the file -- the magic number
    s = f.read(4)
    f.close()

    # Return "" if not at least 4 bytes
    if len(s) != 4:
        return ""

    # Convert to 4-byte int in native byte order -- return "" if impossible
    try:
        (magic,) = struct.unpack("=l", s)
    except struct.error:
        return ""

    # Check for GNU dbm
    if magic == 0x13579ace:
        return "gdbm"

    # Check for BSD hash
    if magic == 0x061561:
        return "dbhash"

    # Unknown
    return ""

"""Guess which db package to use to open a db file."""

import struct

def whichdb(filename):
    """Guess which db package to use to open a db file.

    Return values:

    - None if the database file can't be read;
    - empty string if the file can be read but can't be recognized
    - the module name (e.g. "dbm" or "gdbm") if recognized.

    Importing the given module may still fail, and opening the
    database using that module may still fail.
    """

    # Check for dbm first -- this has a .pag and a .dir file
    try:
        f = open(filename + ".pag", "rb")
        f.close()
        f = open(filename + ".dir", "rb")
        f.close()
        return "dbm"
    except IOError:
        pass

    # See if the file exists, return None if not
    try:
        f = open(filename, "rb")
    except IOError:
        return None

    # Read the first 4 bytes of the file -- the magic number
    s = f.read(4)
    f.close()

    # Return "" if not at least 4 bytes
    if len(s) != 4:
        return ""

    # Convert to 4-byte int in native byte order -- return "" if impossible
    try:
        (magic,) = struct.unpack("=l", s)
    except struct.error:
        return ""

    # Check for GNU dbm
    if magic == 0x13579ace:
        return "gdbm"

    # Check for BSD hash
    if magic in (0x00061561, 0x61150600):
        return "dbhash"

    # Unknown
    return ""

Support byte-swapped dbhash (bsddb) files. Found by Ben Sayer.
Support byte-swapped dbhash (bsddb) files.  Found by Ben Sayer.

  """Guess which db package to use to open a db file."""
  
  import struct
  
  def whichdb(filename):
      """Guess which db package to use to open a db file.
  
      Return values:
  
      - None if the database file can't be read;
      - empty string if the file can be read but can't be recognized
      - the module name (e.g. "dbm" or "gdbm") if recognized.
  
      Importing the given module may still fail, and opening the
      database using that module may still fail.
      """
  
      # Check for dbm first -- this has a .pag and a .dir file
      try:
          f = open(filename + ".pag", "rb")
          f.close()
          f = open(filename + ".dir", "rb")
          f.close()
          return "dbm"
      except IOError:
          pass
  
      # See if the file exists, return None if not
      try:
          f = open(filename, "rb")
      except IOError:
          return None
  
      # Read the first 4 bytes of the file -- the magic number
      s = f.read(4)
      f.close()
  
      # Return "" if not at least 4 bytes
      if len(s) != 4:
          return ""
  
      # Convert to 4-byte int in native byte order -- return "" if impossible
      try:
          (magic,) = struct.unpack("=l", s)
      except struct.error:
          return ""
  
      # Check for GNU dbm
      if magic == 0x13579ace:
          return "gdbm"
  
      # Check for BSD hash
-     if magic == 0x061561:
+     if magic in (0x00061561, 0x61150600):
          return "dbhash"
  
      # Unknown
      return ""
  
Support byte-swapped dbhash (bsddb) files. Found by Ben Sayer.
## Code Before:
"""Guess which db package to use to open a db file."""

import struct

def whichdb(filename):
    """Guess which db package to use to open a db file.

    Return values:

    - None if the database file can't be read;
    - empty string if the file can be read but can't be recognized
    - the module name (e.g. "dbm" or "gdbm") if recognized.

    Importing the given module may still fail, and opening the
    database using that module may still fail.
    """

    # Check for dbm first -- this has a .pag and a .dir file
    try:
        f = open(filename + ".pag", "rb")
        f.close()
        f = open(filename + ".dir", "rb")
        f.close()
        return "dbm"
    except IOError:
        pass

    # See if the file exists, return None if not
    try:
        f = open(filename, "rb")
    except IOError:
        return None

    # Read the first 4 bytes of the file -- the magic number
    s = f.read(4)
    f.close()

    # Return "" if not at least 4 bytes
    if len(s) != 4:
        return ""

    # Convert to 4-byte int in native byte order -- return "" if impossible
    try:
        (magic,) = struct.unpack("=l", s)
    except struct.error:
        return ""

    # Check for GNU dbm
    if magic == 0x13579ace:
        return "gdbm"

    # Check for BSD hash
    if magic == 0x061561:
        return "dbhash"

    # Unknown
    return ""

## Instruction:
Support byte-swapped dbhash (bsddb) files. Found by Ben Sayer.
## Code After:
"""Guess which db package to use to open a db file."""

import struct

def whichdb(filename):
    """Guess which db package to use to open a db file.

    Return values:

    - None if the database file can't be read;
    - empty string if the file can be read but can't be recognized
    - the module name (e.g. "dbm" or "gdbm") if recognized.

    Importing the given module may still fail, and opening the
    database using that module may still fail.
    """

    # Check for dbm first -- this has a .pag and a .dir file
    try:
        f = open(filename + ".pag", "rb")
        f.close()
        f = open(filename + ".dir", "rb")
        f.close()
        return "dbm"
    except IOError:
        pass

    # See if the file exists, return None if not
    try:
        f = open(filename, "rb")
    except IOError:
        return None

    # Read the first 4 bytes of the file -- the magic number
    s = f.read(4)
    f.close()

    # Return "" if not at least 4 bytes
    if len(s) != 4:
        return ""

    # Convert to 4-byte int in native byte order -- return "" if impossible
    try:
        (magic,) = struct.unpack("=l", s)
    except struct.error:
        return ""

    # Check for GNU dbm
    if magic == 0x13579ace:
        return "gdbm"

    # Check for BSD hash
    if magic in (0x00061561, 0x61150600):
        return "dbhash"

    # Unknown
    return ""
