Pointer
assign · s

Warning

Use this class only when writing HOC code or (in Python) when interacting with legacy code.

In Python, NEURON pointers can be assigned to a variable and manipulated directly; this class was created as a work-around for HOC which does not permit assigning pointers to a variable.

Pointer Class

class Pointer
Syntax:

n.Pointer(_ref_x)

n.Pointer("variable")

n.Pointer(_ref_x, "stmt that may contain $1")

n.Pointer("variable", "stmt that may contain $1 or variable name")

Example:

>>> p = n.Pointer(n._ref_t)
>>> p.val
0.0
>>> p.assign(42)
42.0
>>> n.t
42.0
>>> p.val = 13
>>> n.t
13.0
Description:

Holds a reference to a variable. When memory for the variable is freed, the Pointer will return an error if used.

The optional second arg is used by Pointer.assign() and is described there.

Warning

The string variable arguments refer to HOC variable names not Python variable names. See Pointer.s() for an example.

Syntax:

Pointer(&x)

Pointer("variable")

Pointer(&x, "stmt that may contain $1")

Pointer("variable", "stmt that may contain $1 or variable name")

Description:

Holds a reference to a variable. When memory for the variable is freed, the Pointer will return an error if used.

See Pointer.assign() for the meaning of the optional second arg.

Pointer.val
Syntax:

x = ptr.val

ptr.val = expr

Description:

Returns the value of the variable pointed to by ptr or, if the left hand side of an assignment, sets the value of the variable. See the example in the constructor.

Syntax:

x = ptr.val

ptr.val = expr

Description:

Returns the value of the variable pointed to by ptr or, if the left hand side of an assignment, sets the value of the variable.

Pointer.s()
Syntax:

str = ptr.s()

Description:

If the Pointer was constructed with the name of a variable, that name can be retrieved as a string.

Example:

>>> n('create soma')
1
>>> p = n.Pointer('soma.v(0.5)')
>>> p.s()
'soma.v(0.5)'
Syntax:

str = ptr.s

Description:

If the Pointer was constructed with the name of a variable, that name can be retrieved as a strdef.

Pointer.assign()
Syntax:

x = ptr.assign(val)

Description:

Sets the value of the pointer variable to val. If prt was constructed with a second arg then the execution depends on its form. If the second arg string contains one or more $1 tokens, then the tokens are replaced by hoc_ac_, hoc_ac_ is set to the val and the resulting statement is executed. Otherwise the second arg string is assumed to be a variable name and a statement of the form variablename = hoc_ac_ is executed. Note that the compiling of these statements takes place just once when the Pointer is constructed. Thus ptr.assign(val) is marginally faster than execute(“stmt with val”).

Returns val.

Syntax:

x = ptr.assign(val)

Description:

Sets the value of the pointer variable to val. If prt was constructed with a second arg then the execution depends on its form. If the second arg string contains one or more $1 tokens, then the tokens are replaced by hoc_ac_, hoc_ac_ is set to the val and the resulting statement is executed. Otherwise the second arg string is assumed to be a variable name and a statement of the form variablename = hoc_ac_ is executed. Note that the compiling of these statements takes place just once when the Pointer is constructed. Thus ptr.assign(val) is marginally faster than execute(“stmt with val”).

(following not implemented) And if the stmt is a variablename then the pointer is used and all interpreter overhead is avoided. Also note that on construction, the second arg variable is executed with the value of the first arg pointer. So

Returns val.