How to find Version of Qt?

How do I know which version of Qt I am using? When I open Qt Creator it shows "Welcome to Qt Creator 2.3". In the build setting, however, it shows Qt Version 4.7.1.

qmake-qt5 --version

or

qmake --version

Starting with Qt 5.3 you can use:

qtdiag

This prints a bunch of useful information. The first line includes the version:

Qt 5.5.1 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 5.3.1 20160407) on "xcb" 

All the version info is in PyQt5.Qt:

import inspect
from PyQt5 import Qt

vers = ['%s = %s' % (k,v) for k,v in vars(Qt).items() if k.lower().find('version') >= 0 and not inspect.isbuiltin(v)]
print('\n'.join(sorted(vers)))

prints

PYQT_VERSION = 328193
PYQT_VERSION_STR = 5.2.1
QOpenGLVersionProfile = <class 'PyQt5.QtGui.QOpenGLVersionProfile'>
QT_VERSION = 328192
QT_VERSION_STR = 5.2.0
qVersion = <built-in function qVersion>
qWebKitMajorVersion = <built-in function qWebKitMajorVersion>
qWebKitMinorVersion = <built-in function qWebKitMinorVersion>
qWebKitVersion = <built-in function qWebKitVersion>

The functions can be called too:

>>> vers = ['%s = %s' % (k,v()) for k,v in vars(Qt).items() if k.lower().find('version') >= 0 and inspect.isbuiltin(v)]
>>> print('\n'.join(sorted(vers)))
qVersion = 5.2.0
qWebKitMajorVersion = 538
qWebKitMinorVersion = 1
qWebKitVersion = 538.1