Coding and Decoding in Python

Discussion in 'Python' started by Wanderer, Mar 17, 2011.

  1. Wanderer

    Wanderer Guest

    I have a dll that to communicate with I need to send numeric codes. So
    I created a dictionary. It works in one direction in that I can
    address the key and get the value. But when the program returns the
    value I can't get the key. This code is very simple and I could use a
    list and the index except for the last value. Is there a better way to
    handle coding and decoding values to strings?

    QCam_Info = {
    'qinfCameraType' : 0, # Camera model (see
    QCam_qcCameraType)
    'qinfSerialNumber' : 1, # Deprecated
    'qinfHardwareVersion' : 2, # Hardware version
    'qinfFirmwareVersion' : 3, # Firmware version
    'qinfCcd' : 4, # CCD model (see
    QCam_qcCcd)
    'qinfBitDepth' : 5, # Maximum bit depth
    'qinfCooled' : 6, # Returns 1 if
    cooler is available, 0 if not
    'qinfReserved1' : 7, # Reserved
    'qinfImageWidth ' : 8, # Width of the ROI (in
    pixels)
    'qinfImageHeight' : 9, # Height of the ROI (in
    pixels)
    'qinfImageSize' : 10, # Size of returned
    image (in bytes)
    'qinfCcdType' : 11, # CDD type (see
    QCam_qcCcdType)
    'qinfCcdWidth' : 12, # CCD maximum width
    'qinfCcdHeight' : 13, # CCD maximum height
    'qinfFirmwareBuild' : 14, # Build number of the
    firmware
    'qinfUniqueId' : 15, # Same as uniqueId
    in QCam_CamListItem
    'qinfIsModelB' : 16, # Cameras
    manufactured after March 1, 2004 return 1, otherwise 0
    'qinfIntensifierModel' : 17, # Intensifier tube
    model (see QCam_qcIntensifierModel)
    'qinfExposureRes' : 18, # Exposure time
    resolution (nanoseconds)
    'qinfTriggerDelayRes' : 19, # Trigger delay
    Resolution (nanoseconds)
    'qinfStreamVersion' : 20, # Streaming version
    'qinfNormGainSigFigs' : 21, # Normalized Gain
    Significant Figures resolution
    'qinfNormGaindBRes' : 22, # Normalized Gain dB
    resolution (in micro units)
    'qinfNormITGainSigFigs' : 23, # Normalized Intensifier
    Gain Significant Figures
    'qinfNormITGaindBRes' : 24, # Normalized Intensifier
    Gain dB resolution (micro units)
    'qinfRegulatedCooling' : 25, # 1 if camera has
    regulated cooling
    'qinfRegulatedCoolingLock' : 26, # 1 if camera is at
    regulated temperature, 0 otherwise
    'qinfFanControl' : 29, # 1 if camera can
    control fan speed
    'qinfHighSensitivityMode' : 30, # 1 if camera has high
    sensitivity mode available
    'qinfBlackoutMode' : 31, # 1 if camera has
    blackout mode available
    'qinfPostProcessImageSize' : 32, # Returns the size (in
    bytes) of the post-processed image
    'qinfAsymmetricalBinning' : 33, # 1 if camera has
    asymmetrical binning (ex: 2x4)
    'qinfEMGain' : 34, # 1 if EM gain is
    supported, 0 if not
    'qinfOpenDelay' : 35, # 1 if shutter open
    delay controls are available, 0 if not
    'qinfCloseDelay' : 36, # 1 if shutter close
    delay controls are available, 0 if not
    'qinfColorWheelSupported' : 37, # 1 if color wheel is
    supported, 0 if not
    'qinfReserved2' : 38,
    'qinfReserved3' : 39,
    'qinfReserved4' : 40,
    'qinfReserved5' : 41,
    'qinfEasyEmModeSupported' : 42, # 1 if camera supports
    Easy EM mode
    'qinfLockedGainModeSupported' : 43,
    'qinf_last' : 44,
    '_qinf_force32' : 0xFFFFFFFF
    }
     
    Wanderer, Mar 17, 2011
    #1
    1. Advertisements

  2. Wanderer

    Mel Guest

    [ ... ]
    '_qinf_force32' : 0xFFFFFFFF
    I handled this problem in a kind of cheap, nasty way with (untested)

    for k, v in QCam_Info.items():
    QCam_Info[v] = k

    Then the dictionary lookups work both ways.

    Mel.
     
    Mel, Mar 17, 2011
    #2
    1. Advertisements

  3. Wanderer

    John Gordon Guest

    What happens when two keys have the same value? How would you know which
    key to return?

    In your sample code all the values are different, but surely that won't
    always be the case with real data.
     
    John Gordon, Mar 17, 2011
    #3
  4. Wanderer

    Wanderer Guest

    I guess two keys having the same value is why dictionaries don't
    return keys for values, but this is a code. Each value has a unique
    meaning to both sender and receiver. The text part is for making the
    program understandable and printing understandable error messages.
     
    Wanderer, Mar 17, 2011
    #4
  5. Wanderer

    John Gordon Guest

    I see. You're storing integer equivalents for the labels themselves,
    not the actual data associated with the labels.

    Then Mel's solution is a good one -- construct a second dict which
    has the keys and values swapped.
     
    John Gordon, Mar 17, 2011
    #5
  6. If you only have a few keys:

    def find_key(value, d):
    """Return the key in dictionary d that has the given value.
    If there are multiple keys with the same value, return an
    arbitrarily chosen one."""
    for k, v in d.items():
    if v == value: return k
    raise KeyError('no such value found')


    If you have many keys/values, then simply create a reverse dictionary:

    Rev_QCam_Info = {}
    for key, value in QCam_Info.items():
    Rev_QCam_Info[value] = key

    and then search that.
     
    Steven D'Aprano, Mar 18, 2011
    #6
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.