versbose_eval prints metric at each iteration even if its value is an integer with Python api.

[jfpuget]

verbose_eval not None creates an evaluation monitor whatever the value of verbose_eval.

        if verbose_eval:
            callbacks.append(callback.EvaluationMonitor())

According to documentation it should print something only N iterations if verbose_eval value is an integer N.

[jfpuget]

Workaround:

monitor = xgb.callback.print_evaluation(period=verbose_eval)

and use callback argument to training api.