Python code to read registry

Documentation says that EnumKey returns string with key's name. You have to explicitly open it with _winreg.OpenKey function. I've fixed your code snippet:

from _winreg import *

aKey = r"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall"
aReg = ConnectRegistry(None, HKEY_LOCAL_MACHINE)

print(r"*** Reading from %s ***" % aKey)

aKey = OpenKey(aReg, aKey)
for i in range(1024):
    try:
        asubkey_name = EnumKey(aKey, i)
        asubkey = OpenKey(aKey, asubkey_name)
        val = QueryValueEx(asubkey, "DisplayName")
        print(val)
    except EnvironmentError:
        break

Please note, that not every key has "DisplayName" value available.

What about x86 on x64? Use 64-bit Specific Types

What if there's more than 1024 sub-keys in "Uninstall"? Use _winreg.QueryInfoKey(key)

Python 2:

import errno, os, _winreg
proc_arch = os.environ['PROCESSOR_ARCHITECTURE'].lower()
proc_arch64 = os.environ['PROCESSOR_ARCHITEW6432'].lower()

if proc_arch == 'x86' and not proc_arch64:
    arch_keys = {0}
elif proc_arch == 'x86' or proc_arch == 'amd64':
    arch_keys = {_winreg.KEY_WOW64_32KEY, _winreg.KEY_WOW64_64KEY}
else:
    raise Exception("Unhandled arch: %s" % proc_arch)

for arch_key in arch_keys:
    key = _winreg.OpenKey(_winreg.HKEY_LOCAL_MACHINE, r"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall", 0, _winreg.KEY_READ | arch_key)
    for i in xrange(0, _winreg.QueryInfoKey(key)[0]):
        skey_name = _winreg.EnumKey(key, i)
        skey = _winreg.OpenKey(key, skey_name)
        try:
            print _winreg.QueryValueEx(skey, 'DisplayName')[0]
        except OSError as e:
            if e.errno == errno.ENOENT:
                # DisplayName doesn't exist in this skey
                pass
        finally:
            skey.Close()

Python 3:

import errno, os, winreg
proc_arch = os.environ['PROCESSOR_ARCHITECTURE'].lower()
proc_arch64 = os.environ['PROCESSOR_ARCHITEW6432'].lower()

if proc_arch == 'x86' and not proc_arch64:
    arch_keys = {0}
elif proc_arch == 'x86' or proc_arch == 'amd64':
    arch_keys = {winreg.KEY_WOW64_32KEY, winreg.KEY_WOW64_64KEY}
else:
    raise Exception("Unhandled arch: %s" % proc_arch)

for arch_key in arch_keys:
    key = winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, r"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall", 0, winreg.KEY_READ | arch_key)
    for i in range(0, winreg.QueryInfoKey(key)[0]):
        skey_name = winreg.EnumKey(key, i)
        skey = winreg.OpenKey(key, skey_name)
        try:
            print(winreg.QueryValueEx(skey, 'DisplayName')[0])
        except OSError as e:
            if e.errno == errno.ENOENT:
                # DisplayName doesn't exist in this skey
                pass
        finally:
            skey.Close()

As it says in the _winreg.QueryValueEx documentation, you need to pass an already open key. EnumKey returns a string, not an open key.

aReg = ConnectRegistry(None,HKEY_LOCAL_MACHINE)
aKey = OpenKey(aReg, r"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall")
for i in range(1024):
    try:
        keyname = EnumKey(aKey, i)
        asubkey = OpenKey(aKey, keyname)
        val = QueryValueEx(asubkey, "DisplayName")
        print val
    except WindowsError:
        break