Python netsnmp what is the difference between SNMP options?

Question

Python

Good afternoon.
You need to pull the brand and firmware version from the heap of D-link switches.
Installed Python 2.7.6, python-netsnmp 5.7.2
Model shrinks fine:

netsnmp.snmpwalk(".1.3.6.1.2.1.1.1.0", DestHost="10.0.27.35", Community="public")
('DES-3200-26/C1 Fast Ethernet Switch',)

But the firmware refuses:

netsnmp.snmpwalk(".1.3.6.1.2.1.16.19.2.0", DestHost="10.0.27.35", Community="public")
()
netsnmp.snmpgetnext(".1.3.6.1.2.1.16.19.2.0", DestHost="10.0.27.35", Community="public")
('\x80\x00\x00\xab\x03\xbc\xf6\x85\xfa{\xa0',)
netsnmp.snmpget(".1.3.6.1.2.1.16.19.2.0", DestHost="10.0.27.35", Community="public")
(None,)

Although from bashash it gives the firmware normally:

snmpwalk -v2c -O qn -c public 10.0.27.35 1.3.6.1.2.1.16.19
.1.3.6.1.2.1.16.19.1.0 "F0 40 00 20 "
.1.3.6.1.2.1.16.19.2.0 "4.37.B011"
.1.3.6.1.2.1.16.19.3.0 "C1"
.1.3.6.1.2.1.16.19.5.0 1
.1.3.6.1.2.1.16.19.6.0 ""
.1.3.6.1.2.1.16.19.7.0 0.0.0.0
.1.3.6.1.2.1.16.19.8.0 1
.1.3.6.1.2.1.16.19.9.0 2
.1.3.6.1.2.1.16.19.11.1.1.5121 10.0.27.35
.1.3.6.1.2.1.16.19.11.1.2.5121 255.255.255.0
.1.3.6.1.2.1.16.19.11.1.3.5121 1
.1.3.6.1.2.1.16.19.12.0 10.0.27.1

From here a few questions:
1. What kind of nonsense? Why is one parameter given and the other not?
2. What is the difference between snmpwalk, snmpget, snmpgetnext? why is the result different?