---
jupytext:
  text_representation:
    extension: .md
    format_name: myst
    format_version: 1.0.0
    jupytext_version: 1.16.1
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+++ {"tags": ["jupyterlite_sphinx_strip"]}

```{include} header.md

```

# Gotchas

PyWavelets utilizes `NumPy` under the hood. That's why handling the data
that contains `None` values can be surprising. `None` values are converted to
'not a number' (`numpy.nan`) values:

```{code-cell}
import numpy, pywt
x = [None, None]
mode = 'symmetric'
wavelet = 'db1'
cA, cD = pywt.dwt(x, wavelet, mode)
```

The results are:

```{code-cell}
numpy.all(numpy.isnan(cA))
```

<!-- True -->

```{code-cell}
numpy.all(numpy.isnan(cD))
```

<!-- True -->

```{code-cell}
rec = pywt.idwt(cA, cD, wavelet, mode)
numpy.all(numpy.isnan(rec))
```

<!-- True -->