Fixes for Python 3.7 (#972)

* Remove use of position-only parameter syntax
* Remove usage of `typing.Literal`

(both require Python 3.8)

Author: gmgunter

python/packages/isce3/unwrap/snaphu.py

@@ -3,25 +3,13 @@
 import pathlib
 import tempfile
 from dataclasses import dataclass
-from typing import Literal, Optional, Union
+from typing import Optional, Union
 
 import isce3
 import numpy as np
 from pybind_isce3.unwrap import _snaphu_unwrap
 
 
-TransmitMode = Literal["pingpong", "repeat_pass", "single_antenna_transmit"]
-TransmitMode.__doc__ = """Radar transmit mode
-
-    'pingpong' and 'repeat_pass' modes indicate that both antennas both
-    transmitted and received. Both modes have the same effect in the algorithm.
-
-    'single_antenna_transmit' indicates that a single antenna was used to
-    transmit while both antennas received. In this mode, the baseline is
-    effectively halved.
-    """
-
-
 @dataclass(frozen=True)
 class TopoCostParams:
     r"""Configuration parameters for SNAPHU "topo" cost mode
@@ -159,7 +147,7 @@ class TopoCostParams:
     range_res: float
     az_res: float
     wavelength: float
-    transmit_mode: TransmitMode
+    transmit_mode: str
     altitude: float
     earth_radius: float = 6_378_000.0
     kds: float = 0.02
@@ -656,7 +644,7 @@ def tostring(self):
 
 
 @contextlib.contextmanager
-def scratch_directory(d: Optional[os.PathLike] = None, /) -> pathlib.Path:
+def scratch_directory(d: Optional[os.PathLike] = None) -> pathlib.Path:
     """Context manager that creates a (possibly temporary) filesystem directory
 
     If the input is a path-like object, a directory will be created at the
@@ -772,9 +760,6 @@ def from_flat_file(
         raster.data[i0:i1] = mmap[i0:i1]
 
 
-CostMode = Literal["topo", "defo", "smooth", "p-norm"]
-CostMode.__doc__ = """SNAPHU cost mode options"""
-
 CostParams = Union[
     TopoCostParams, DefoCostParams, SmoothCostParams, PNormCostParams,
 ]
@@ -787,7 +772,7 @@ def unwrap(
     igram: isce3.io.gdal.Raster,
     corr: isce3.io.gdal.Raster,
     nlooks: float,
-    cost: CostMode = "smooth",
+    cost: str = "smooth",
     cost_params: Optional[CostParams] = None,
     pwr: Optional[isce3.io.gdal.Raster] = None,
     mask: Optional[isce3.io.gdal.Raster] = None,

tests/python/packages/isce3/unwrap/snaphu.py

@@ -131,7 +131,7 @@ def next_power_of_two(n):
     return z[:length, :width]
 
 
-def jaccard_similarity(a, b, /):
+def jaccard_similarity(a, b):
     """Compute the Jaccard similarity coefficient (intersect-over-union) of two
     boolean arrays.