homework and exercises - Can two bodies of different mass attached at ends of string passed over a frictionless pulley produce equal tension on both sides?

In my textbook there is given a case that to calculate acceleration and tension produced in string when string is attached at it's ends with two bodies of masses such that $m1>m2$ and the tension produced at both ends as reaction to the weight is $T$. How can be tension equal at both ends however the acting force (weight of the bodies) are different?