print(nest.GetConnections(synapse_model="stdp_synapse_exc").get().keys())
dict_keys(['Kplus', 'delay', 'port', 'receptor',
'sizeof', 'source', 'synapse_id', 'synapse_model',
'target', 'target_thread', 'weight'])
we have only these properties .I haven't found lambda here.
This is the synapse model I'm using
nest.CopyModel("stdp_synapse_hom", "stdp_synapse_exc",
{"weight":gmax,"alpha":1,"Wmax":gmax, "tau_plus":
20.0,"lambda": -0.0005, "mu_minus": 0, "mu_plus": 0})