Get and set knob values #nuke

get_set_values.py

# Get all nodes of type Read
readnodes = nuke.allNodes('Read')
for readnode in readnodes:
    print readnode

# List all knobs for selected node
print( nuke.toNode('Read1') )
# List all knobs for specific node
print( nuke.selectedNode() )

# Get value from specific node
value = nuke.toNode('Read1').knob('file').getValue()
# Get value from selected node
value = nuke.selectedNode().knob('file').getValue()
# Get value from this node
value = nuke.thisNode().knob('file').getValue()
# Get value from specific node and evaluate it (good for expressions)
value = nuke.toNode('Read1').knob('file').evaluate()

# Set specific node's value
nuke.toNode('Read1').knob('file').setValue('c:/hello.tif')
# Set selected node's value
nuke.selectedNode().knob('file').setValue('c:/hello.tif')
# Set this node's value
nuke.thisNode().knob('file').setValue('c:/hello.tif')

# Set specific node's knob to default value
nuke.toNode('Grade1').knob('gamma').setValue( nuke.toNode('Grade1').knob('gamma').defaultValue() )

so the problem is its not working when i set #folder by expression link it giving error like this:

# Result: Traceback (most recent call last):
  File "<string>", line 4, in <module>
TypeError: 'bool' object is not iterable

• so i tried to print folder value as string to an other variable but it didnt work