fix: const-qualify data input in dwt

Closes #839

Author: jhossbach

pywt/_extensions/_dwt.pyx

@@ -23,7 +23,7 @@ cpdef dwt_coeff_len(size_t data_len, size_t filter_len, MODE mode):
 
     return common.dwt_buffer_length(data_len, filter_len, mode)
 
-cpdef dwt_single(cdata_t[::1] data, Wavelet wavelet, MODE mode):
+cpdef dwt_single(const cdata_t[::1] data, Wavelet wavelet, MODE mode):
     cdef size_t output_len = dwt_coeff_len(data.size, wavelet.dec_len, mode)
     cdef np.ndarray cA, cD
     cdef int retval_a, retval_d

pywt/tests/test_dwt_idwt.py

@@ -241,6 +241,12 @@ def test_dwt_zero_size_axes():
     assert_raises(ValueError, pywt.dwt, x, 'db2', axis=0)
 
 
+def test_dwt_readonly_array():
+    data = np.random.randn(1000).astype(np.float64)
+    data.setflags(write=False)
+    pywt.dwt(data, "db4")
+
+
 def test_pad_1d():
     x = [1, 2, 3]
     assert_array_equal(pywt.pad(x, (4, 6), 'periodization'),

pywt/tests/test_multilevel.py

@@ -76,6 +76,12 @@ def test_wavedec():
     assert_(pywt.dwt_max_level(len(x), db1) == 3)
 
 
+def test_wavedec_readonly_array():
+    data = np.random.randn(1000).astype(np.float64)
+    data.setflags(write=False)
+    pywt.wavedec(data, "db4", level=2)
+
+
 def test_waverec_invalid_inputs():
     # input must be list or tuple
     assert_raises(ValueError, pywt.waverec, np.ones(8), 'haar')