Which of the following represents an integer in Python?

In Python, an integer is a whole number that does not contain a decimal point. The correct representation of an integer from the given options is 12.

This is distinct from the other options:

1. The first option, 1.2, is a floating-point number because it includes a decimal point, which signifies a real number, not an integer.

2. The second option, 'twelve', is a string because it is enclosed in quotes, representing text rather than a numeric value.

3. The last option, True, is a Boolean value. In Python, while it can be evaluated in a numeric context (where True is considered as 1), it is not an integer in its native form.

Therefore, 12 stands out as the only option that directly and unequivocally matches the definition of an integer in Python.