Example on how to call `Circuit.rename_units`

[jvdwetering]

I'm trying to change register names in a pytket circuit so that I can save to qasm. It tells me I should call rename_units to do that, I however can't figure out how I should actually call this.

TypeError: rename_units(): incompatible function arguments. The following argument types are supported:
    1. rename_units(self, map: collections.abc.Mapping[pytket._tket.unit_id.UnitID | pytket._tket.unit_id.Qubit | pytket._tket.unit_id.Bit, pytket._tket.unit_id.UnitID | pytket._tket.unit_id.Qubit | pytket._tket.unit_id.Bit]) -> bool

Invoked with types: pytket._tket.circuit.Circuit, dict

What should this mapping be? Should it map from these types to strings? Or to something else? Can I give it a dict that only renames some of the units, or must it contain everything? And shouldn't there be a corresponding method get_units() so you can just take that output and modify it?

Here's what I tried:

a = circ.get_q_register("a[q[0]]")
l = a.to_list()
d = {q: f"f{i}" for i, q in enumerate(l)}
circ.rename_units(d)

Looks like if I call it with {q:q} then it doesn't fail, but it obviously doesn't change anything. I can't however change the name in the qubits because they don't have setters, so I'm not sure how I'm supposed to change the name in these registers in these cases.

[CalMacCQ]

Hi, sorry I missed this issue.

We do have one example on the usage of Circuit.rename_units in the Registers and Ids section of the user manual. If you scroll a little, you should find it. It should probably be more findable than it is.

I'll explain the example here for clarity.

from pytket import Circuit, Qubit, Bit

# create a Circuit with two qubits and two bits
# These units have the default names "q" and "c" respectively
circ = Circuit(2, 2)
circ.add_qubit(Qubit("a", 0)) # add a qubit with the name "a"
print(circ.bits)
print(circ.qubits)

Output:

[c[0], c[1]]
[a[0], q[0], q[1]]

Now suppose I want to change the name of the "a" qubit to the default "q" name. I can make a key:value pair for the rename. The key for this mapping is the UnitID that we want to rename (a UnitID is essentially a Union of the Qubit and Bit type). The mapping can also be partial so you don't have to put every single UnitID in the mapping.

qubit_map = {
    Qubit("a", 0) : Qubit(3), # If no name is given to the `Qubit` constructor, the "q" name is used.
    Qubit(1) : Qubit("a", 0), # Rename q[1] to a[0]
    Bit(0) : Bit("z", [0, 1]), # Rename c[0] to z[0, 1]
}
circ.rename_units(qubit_map)
print(circ.qubits)
print(circ.bits)

Output:

[a[0], q[0], q[3]]
[c[1], z[0, 1]]

I hope this helps. If you have any follow up queries then let me know :)