Using flags can be frustrating because not all flags are easily accessed or documented. Create a flags.py file and you have a simple way to easily get at them. Thanks to Nathan and Dee for the tip on where to find them. I'm not sure what context you would use all these or if they are all valid from within python, but the flags I've used from here all work.

 

General flags (must not intersect any class-specific flags):

General knob flags begin at 0x80.
 


DISABLED                  = 0x0000000000000080; ///< Grey out and lock interface. Prevents copy/paste (see READ_ONLY to allow this).
NO_ANIMATION              = 0x0000000000000100; ///< Disable right click and button animation menu.
DO_NOT_WRITE              = 0x0000000000000200; ///< Disables calling to_script. No writing to script file or copy/paste.
INVISIBLE                 = 0x0000000000000400; ///< Disables param and viewer widgets. Cannot be made visible again. See HIDDEN for this.
RESIZABLE                 = 0x0000000000000800; ///< Allows more complex knobs to resize param panel to fill available space.
STARTLINE                 = 0x0000000000001000; ///< Start a new line in the param panel before knob widget.
ENDLINE                   = 0x0000000000002000; ///< Start a new line in the param panel after knob widget.
NO_RERENDER               = 0x0000000000004000; ///< Removes knob from Op hash calculation, preventing rerendering on value change.
NO_HANDLES                = 0x0000000000008000; ///< Disables viewer widget handles from drawing.
KNOB_CHANGED_ALWAYS       = 0x0000000000010000; ///< Always calls knob_changed, regardless of whether it has previously returned false.
NO_KNOB_CHANGED           = 0x0000000000020000; ///< Prevents knob_changed being called on value change. Set if prev knob_changed returned false.
HIDDEN                    = 0x0000000000040000; ///< Disables param panel and viewer widgets. Can be managed dynamically with show/hide.
NO_UNDO                   = 0x0000000000080000; ///< Disables laying down of undo/redo points.
ALWAYS_SAVE               = 0x0000000000100000; ///< Forces data to always be written regardless. Deprecated. Override not_default instead.
NODE_KNOB                 = 0x0000000000200000; ///< For internal use only.
HANDLES_ANYWAY            = 0x0000000000400000; ///< Force viewer widgets to be visible regardless of current node tab.
INDETERMINATE             = 0x0000000000800000; ///< Presents a blacked out undefined value interface on supporting knobs.
COLOURCHIP_HAS_UNSET      = 0x0000000001000000; ///< Defines whether a color chip can be in the 'unset' state. Defaults to false.
SMALL_UI                  = 0x0000000002000000; ///< Switches param panel widget to be more viewer Toolbar friendly in supported knobs (eg Button).
NO_NUMERIC_FIELDS         = 0x0000000004000000; ///< Disables numeric input box widget on supported knobs.
KNOB_CHANGED_RECURSIVE    = 0x0000000008000000; ///< Recursive knob_changed calls are prevented unless overriden using this flag.
READ_ONLY                 = 0x0000000010000000; ///< As with DISABLED, except value can be copied from and expression linked against.
NO_CURVE_EDITOR           = 0x0000000020000000; ///< Disables curve editor.
NO_MULTIVIEW              = 0x0000000040000000; ///< Disables view menu and splitting when in a multiview script.
EARLY_STORE               = 0x0000000080000000; ///< Forces early synchronisation of data allowing usage in pre-op calls such as split_input().
MODIFIES_GEOMETRY         = 0x0000000100000000; ///< Should be set on all knobs which modify geometry or associated transforms.
OUTPUT_ONLY               = 0x0000000200000000; ///< Similar to READ_ONLY & NO_RERENDER together - data changes don't count as a script change.
NO_KNOB_CHANGED_FINISHED  = 0x0000000400000000; ///< Prevents knob_changed_finished being called on value change. Set if prev call returned false.
SET_SIZE_POLICY           = 0x0000000800000000; ///< Do not use.
EXPAND_TO_WIDTH           = 0x0000001000000000; ///< Force knob to expand to fill available space. - only for Enum knobs currently
NEVER_DRAW_HANDLES        = 0x0000002000000000; ///< Disables viewer widget handles from drawing. Unlike the NO_HANDLES flag, the state of this flag will never change internally within Nuke
KNOB_CHANGED_RIGHTCONTEXT = 0x0000004000000000; ///< Always call knob_changed on a properly cooked Op, even if KNOB_CHANGED_ALWAYS is on
DONT_SAVE_TO_NODEPRESET   = 0x0000008000000000; ///< This value of this knob should never be saved to a NodePreset. Can be used, for example, for data knobs.
RESERVED_COLORCHIP_KNOB   = 0x0000010000000000; ///< DO NOT USE. This value is used by the colorchip knob.
READ_ONLY_IN_SCRIPTS      = 0x0000020000000000; ///< Prevents knobs from being modified from Python/Tcl
ALWAYS_ALIGN_LABEL_TOP    = 0x0000040000000000; ///< Label is always aligned to the top of the Knob
TINY_SLIDER               = 0x0000080000000000; ///< Modifies SLIDER to be a tiny slider underneath lineedit. Should be a numeric knob flag but we've overrun the < 0x80 condition.
HIDE_ANIMATION_AND_VIEWS  = 0x0000100000000000; ///< Prevents Animation Curve_Knob and Views being shown. Animation is still possible, unless NO_ANIMATION is set of course.
NO_COLOR_DROPDOWN         = 0x0000200000000000; ///< Prevents Color Panel Dropdown from being available. Popup color panel will stil be available.
NODEGRAPH_ONLY            = 0x0000400000000000; ///< Indicate that this knob should only be displayed when using the NodeGraph, since the Timeline uses gpuEngine, which might not support all the same knobs.
NO_SCRIPT_EXECUTE         = 0x0000800000000000; ///< Prevents 'execute' being called on the knob
MODIFIES_TIME             = 0x0001000000000000; ///< Should be set on all knobs which modify timing
TOOLBAR_BUTTON_DRAWSTYLE  = 0x0002000000000000; ///< This knob must be drawn in the style of Viewer toolbar knobs
FLAGS_LOCKED              = 0x0004000000000000; ///< Used to lock modifications to this knobs flags
DO_NOT_READ               = 0x0008000000000000; ///< Skip reading the knob from script, must be set before loading from script Enumeration_Knob only
 
 
Knob type-specific flags:
These should be in the range < 0x80.
 
Numeric knobs:
MAGNITUDE                 = 0x0000000000000001; ///< Enables switchable numeric box & slider to multiple boxes (array knob derived numeric knobs).
SLIDER                    = 0x0000000000000002; ///< Enables slider on single numeric knob, or array knob with MAGNITUDE set (numeric knobs).
LOG_SLIDER                = 0x0000000000000004; ///< Switches linear slider to log slider, or cubic depending on range (numeric knobs with SLIDER).
STORE_INTEGER             = 0x0000000000000008; ///< Stores and presents integer value rather than float (numeric knobs).
FORCE_RANGE               = 0x0000000000000010; ///< Forces stored and presented value to be clamped to range set (numeric knobs).
ANGLE                     = 0x0000000000000020; ///< Switches widget for angle UI (single value numeric knobs).
NO_PROXYSCALE             = 0x0000000000000040; ///< Disables proxyscaling on knobs supporting it (XY_Knob & WH_Knob derivatives).
      
String Knobs:
GRANULAR_UNDO             = 0x0000000000000001; ///< Disables concatenation of minor undo events (string knobs)
NO_RECURSIVE_PATHS        = 0x0000000000000002; ///< Badly named. Actually disables relative paths (string knobs).
NO_TCL_ERROR              = 0x0000000000000004; ///< For strings containing TCL expressions, don't replace with TCL error messages if an error occurs
 
Enumeration:
SAVE_MENU                 = 0x0000000002000000; ///< Forces menu entries to be written to script. Used by dynamic menus (enumeration knobs).
EXPAND_TO_CONTENTS        = 0x0000000000000001; ///< Make Enumeration knobs adjust their width to the size of the largest munu item.
EXACT_MATCH_ONLY          = 0x0000000000000002; ///< Make Enumeration knobs use exact match when setting a value. If an attempt is made to set an
                                                                            ///< invalid value, the knob will be put into an Error state.
STRIP_CASCADE_PREFIX      = 0x0000000000000004; ///< Make Cascading Enumeration knobs not serialise out cascading prefixes
 
SceneView / Path knob:
SINGLE_SELECTION_ONLY     = 0x0000000000000001; ///< Knob only allows one item to be selected at a time
SHOW_BUTTONS              = 0x0000000000000002; ///< Show Add Layer/Delete Layer buttons
SHOW_SCENE_PICK_BUTTON    = 0x0000000000000008; ///< Show Scene Graph Dialog button to choose Prim(s) from the Scene
 
BeginGroup:
CLOSED                    = 0x0000000000000001; ///< Stores the open/closed state of group knobs (group knobs).
TOOLBAR_GROUP             = 0x0000000000000002; ///< Make the group into a viewer toolbar. General used via BeginToolbar (group knobs).
TOOLBAR_LEFT              = 0x0000000000000000; ///< Defines which side of viewer toolbar appears on. Pick one at toolbar construction time (toolbar).
TOOLBAR_TOP               = 0x0000000000000010; ///< Defines which side of viewer toolbar appears on. Pick one at toolbar construction time (toolbar).
TOOLBAR_BOTTOM            = 0x0000000000000020; ///< Defines which side of viewer toolbar appears on. Pick one at toolbar construction time (toolbar).
TOOLBAR_RIGHT             = 0x0000000000000030; ///< Defines which side of viewer toolbar appears on. Pick one at toolbar construction time (toolbar).
TOOLBAR_POSITION          = 0x0000000000000030; ///< A mask for the position part of the flags
 
ChannelSet/Channel:
NO_CHECKMARKS             = 0x0000000000000001; ///< Disable individual channel checkbox widgets (channel/channelset knobs).
NO_ALPHA_PULLDOWN         = 0x0000000000000002; ///< Disable 4th channel pulldown widget (channel/channelset knobs).
FULL_LAYER_ENABLED        = 0x0000000000000004; ///< channel/channelset knobs will always consider every channel in a layer to be enabled.
FORCE_RGBA_LAYER          = 0x0000000000000008; ///< Disables the layer selection dropdown. Forces the layer to always be RGBA.
 
Format knob:
PROXY_DEFAULT             = 0x0000000000000001; ///< Sets default knob value from script proxy format rather than full res (format knob).
 
ColorChip knob:
COLORCHIP_PRESERVE_ALPHA  = 0x0000010000000000; ///< The ColorChip_knob discards alpha values by default. Set this flag to make it keep them, instead.
 
Colorspace Knob:
ALLOW_NUKE_COLORSPACES    = 0x0000000000000001; ///< Allows the knob to display Nuke's native colorspaces if Color Management is set to Nuke.
 
Text knob:
WORD_WRAP                 = 0x0000000000000001; ///< Enable word wrapping-wrapping for the Text_knob
 
Eyedropper knob:
CHECKED                   = 0x0000000000000001; ///< Tick checkbox in the ticker