If you care about preserving the order of your mapping keys, the comment and the white space between the elements of the root-level sequence, e.g. because this file is under revision control, then you should use ruamel.yaml (disclaimer: I am the author of that package).

Assuming your YAML document is in the file input.yaml:

import sys
import ruamel.yaml

yaml = ruamel.yaml.YAML()
# yaml.preserve_quotes = True
with open('input.yaml') as fp:
    data = yaml.load(fp)
for elem in data:
    if elem['name'] == 'sense2':
         elem['value'] = 1234
         break  # no need to iterate further
yaml.dump(data, sys.stdout)

gives:

# Sense 1
- name: sense1
  type: float
  value: 31

# sense 2
- name: sense2
  type: uint32_t
  value: 1234

# Sense 3
- name: sense3
  type: int32_t
  value: 0

- name: sense4
  type: int32_t
  value: 0
- name: sense5
  type: int32_t
  value: 0
- name: sense6
  type: int32_t
  value: 0

If you care about preserving the order of your mapping keys, the comment and the white space between the elements of the root-level sequence, e.g. because this file is under revision control, then you should use ruamel.yaml (disclaimer: I am the author of that package).

Assuming your YAML document is in the file input.yaml:

import sys
import ruamel.yaml

yaml = ruamel.yaml.YAML()
# yaml.preserve_quotes = True
with open('input.yaml') as fp:
    data = yaml.load(fp)
for elem in data:
    if elem['name'] == 'sense2':
         elem['value'] = 1234
         break  # no need to iterate further
yaml.dump(data, sys.stdout)

gives:

# Sense 1
- name: sense1
  type: float
  value: 31

# sense 2
- name: sense2
  type: uint32_t
  value: 1234

# Sense 3
- name: sense3
  type: int32_t
  value: 0

- name: sense4
  type: int32_t
  value: 0
- name: sense5
  type: int32_t
  value: 0
- name: sense6
  type: int32_t
  value: 0

This can safely be used on untrusted YAML. The (default) RoundtripLoader is a subclass of the SafeLoader even though it can handle and preserve tags (which it doesn't interpret in the dangerous way PyYAML does when enabling loading of unregistered tags).