import yaml, json

datos = [
    {"densidad": [0.6, 0.7], "humedad": [0.5, 0.7]},
    {"densidad": [0.66, 0.89], "humedad": [0.4, 0.7]},
    {"densidad": [0.61, 0.74], "humedad": [0.1, 0.7]},
]

print json.dumps(datos, indent=4)

# salida json
"""
[
    {
        "humedad": [
            0.5,
            0.69999999999999996
        ],
        "densidad": [
            0.59999999999999998,
            0.69999999999999996
        ]
    },
    {
        "humedad": [
            0.40000000000000002,
            0.69999999999999996
        ],
        "densidad": [
            0.66000000000000003,
            0.89000000000000001
        ]
    },
    {
        "humedad": [
            0.10000000000000001,
            0.69999999999999996
        ],
        "densidad": [
            0.60999999999999999,
            0.73999999999999999
        ]
    }
]
"""


print yaml.dump(datos, default_flow_style=False)

    # salida yaml
  """
    - densidad:
      - 0.59999999999999998
      - 0.69999999999999996
      humedad:
      - 0.5
      - 0.69999999999999996
    - densidad:
      - 0.66000000000000003
      - 0.89000000000000001
      humedad:
      - 0.40000000000000002
      - 0.69999999999999996
    - densidad:
      - 0.60999999999999999
      - 0.73999999999999999
      humedad:
      - 0.10000000000000001
      - 0.69999999999999996
    """