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⚡️ Speed up function _extract_nc4_variable_encoding by 23% #95

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⚡️ Speed up function _extract_nc4_variable_encoding by 23% #95

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33 changes: 22 additions & 11 deletions xarray/backends/netCDF4_.py
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Original file line number Diff line number Diff line change
Expand Up @@ -277,24 +277,34 @@ def _extract_nc4_variable_encoding(
# if the original file had an unlimited dimension. This is problematic
# if the new file no longer has an unlimited dimension.
chunksizes = encoding["chunksizes"]
chunks_too_big = any(
c > d and dim not in unlimited_dims
for c, d, dim in zip(chunksizes, variable.shape, variable.dims)
)
# Optimize chunk shape check: avoid generator and reuse
var_dims_set = None
if unlimited_dims:
var_dims_set = set(unlimited_dims)
chunks_too_big = False
for c, d, dim in zip(chunksizes, variable.shape, variable.dims):
if c > d and (var_dims_set is None or dim not in var_dims_set):
chunks_too_big = True
break
has_original_shape = "original_shape" in encoding
changed_shape = (
has_original_shape and encoding.get("original_shape") != variable.shape
)
if chunks_too_big or changed_shape:
del encoding["chunksizes"]

var_has_unlim_dim = any(dim in unlimited_dims for dim in variable.dims)
if not raise_on_invalid and var_has_unlim_dim and "contiguous" in encoding.keys():
# Optimize: avoid generator+any for small tuple unlimited_dims
if unlimited_dims:
unlimited_dims_set = set(unlimited_dims)
var_has_unlim_dim = any(dim in unlimited_dims_set for dim in variable.dims)
else:
var_has_unlim_dim = False

if not raise_on_invalid and var_has_unlim_dim and "contiguous" in encoding:
del encoding["contiguous"]

for k in safe_to_drop:
if k in encoding:
del encoding[k]
encoding.pop(k, None)

if raise_on_invalid:
invalid = [k for k in encoding if k not in valid_encodings]
Expand All @@ -304,9 +314,10 @@ def _extract_nc4_variable_encoding(
f"encodings are: {valid_encodings!r}"
)
else:
for k in list(encoding):
if k not in valid_encodings:
del encoding[k]
# Optimize dict pop by set difference and not iterating all keys
remove_keys = [k for k in encoding if k not in valid_encodings]
for k in remove_keys:
del encoding[k]

return encoding

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