Protocol Limitations and FAQ

python-snap7 implements the S7 protocol over TCP/IP. The following operations are not possible with this protocol:

Limitation	Explanation
Read tag/symbol names from PLC	Symbol names exist only in the TIA Portal project file, not in the PLC. The S7 protocol only addresses data by area, DB number, and byte offset.
Get DB structure or layout from PLC	The PLC stores only raw bytes. The structure definition lives in the TIA Portal project. You must define your data layout in your Python code.
Discover PLCs on the network	The classic S7 protocol has no broadcast discovery mechanism. However, python-snap7 provides PROFINET DCP discovery via the s7 discover CLI command (requires pip install python-snap7[discovery]). See Command-Line Interface for details.
Create PLC backups	Full project backup requires TIA Portal. python-snap7 can upload individual blocks, but this is not a complete backup.
S7CommPlus V4	python-snap7 supports S7CommPlus V1, V2, and V3 via the s7 package. V4 is not yet supported. For PLCs that require V4, use OPC UA as an alternative.