Network.initialize(): UnboundLocalError when the Network was constructed with segments

[awickert]

Network.initialize() raises UnboundLocalError whenever the Network was constructed with a list of segments, because segments is bound only inside the branch that builds them.

Reproduction

Against master @ 9724052:

import numpy as np, grlp

seg = grlp.Segment()
net = grlp.Network(segments=[seg])
net.initialize(
    upstream_segment_IDs=[[]], downstream_segment_IDs=[[]],
    x=[np.arange(0., 1000., 100.)], z=[np.linspace(10., 0., 10)],
    Q=[np.ones(10)], B=[np.ones(10)], x_bl=1000., z_bl=0.)

  File "grlp/grlp.py", line 1493, in initialize
    self.segments = segments
                    ^^^^^^^^
UnboundLocalError: cannot access local variable 'segments' where it is not associated with a value

Mechanism

Network.__init__ — L979 accepts segments, and its docstring advertises this as the way to build a network ("Instantiate the Network object with a list of Long Profile objects"). initialize() then defaults to overwrite=False — L1427, so with segments already present it takes the not-rebuilding branch:

_build_segments = True                     # L1469
if self.segments is not None:
    if overwrite:
        print("Overwriting prior network segments.")
    else:
        _build_segments = False            # L1474
...
if _build_segments:                        # L1487
    nseg = len(x)
    segments = []                          # the ONLY binding of `segments`
    for i in range(nseg):
        segments.append( Segment() )
# Class var; clunkier name
self.segments = segments                   # L1493 -- nothing bound on the else path

L1469-L1493

Why nothing catches it

Every test constructs grlp.Network() with no arguments, so the branch is never taken. The ten scripts under examples/deprecated/ that do use grlp.Network(segments) configure the segments by hand and go straight to evolve_threshold_width_river_network() — none of them calls initialize() afterwards. So no shipped code exercises the combination of the segments-passing constructor and initialize(), which is the pair that crashes.

Suggested fix

Bind the existing segments on the else path:

if _build_segments:
    nseg = len(x)
    segments = []
    for i in range(nseg):
        segments.append( Segment() )
else:
    # Not overwriting: reuse the Segment objects already on the Network
    # (passed to __init__). They are re-populated from the arguments below,
    # so "overwrite" governs the objects, not their contents.
    segments = self.segments
# Class var; clunkier name
self.segments = segments

That reading of overwrite — it governs whether the Segment objects are rebuilt, not whether their contents are re-populated — is what makes the rest of initialize() coherent, since the loop below re-applies x, z, Q and B to each segment either way. Worth confirming that is the intent.

One open question the fix does not settle: if len(self.segments) != len(x), the loop below will IndexError. Whether to validate that, and with what message, is a design call rather than part of this bug.

How this was found

Running pyright over this engine — it reports segments as possibly-unbound at L1493 and L1496. Related but separate: #23.

🤖 Generated with Claude Code