{Polchinski Vol.1 Chapter 2 Section 2.4}
We know how the stress tensor transforms under a general CFT which is correctly given by Eq. 2.4.24
$$\epsilon^{-1} \delta T (z) = -\frac{c}{12} \partial_{z}^{3} v(z) - 2\partial_z v(z) T(z) -v(z)\partial_zT(z) \tag{2.4.24}$$
Now from the above expression, how can one get the finite form of the above transformation law given by Eq. 2.4.26 as
$$(\partial w)^2 T(w) = T(z) - \frac{c}{12} \{w,z\} \tag{2.4.26}$$
the second term contains the Schwarzian derivative which tells us about the Weyl anomaly associated with the CFT. However, I don't quite get the form of the Schwarzian derivative which is given by Eq. 2.4.27
$$\{f,z\} = \frac{2\partial_z^3f\partial_zf - 3\partial_z^2f \partial_z^2f}{2\partial_zf \partial_zf}\tag{2.4.27}$$
