The fifth generation of mobile communications (5G) is the new 3GPP technology designed to solve a wide range of requirements. On the one hand, it must be able to support high bit rates and ultra-low latency services, and on the other hand, it should be able to connect a massive amount of devices with loose bandwidth and delay requirements. In this context, as scheduling is always a delicate vendor topic and there are not so many free and complete simulation tools to support all 5G features, in this paper we present Py5cheSim. Py5cheSim is a flexible and open-source simulator based on Python and specially oriented to simulate cell capacity in 3GPP 5G networks and beyond. To the best of our knowledge, Py5cheSim is the first simulator that supports Network Slicing at the Radio Access Network (RAN), one of the main innovations of 5G. The present work describes its design and implementation choices and the principal validation results. Finally, as another contribution, we present an exhaustive analysis of the existing available simulation tools highlighting the novelty of Py5cheSim comparing with the others existing simulation software for 5G.