# Tilde means very different things in Python vs. Matlab!

For those transitioning between Matlab/Octave and Python, the “logical not” tilde `~`

operator of Matlab/Octave is NOT matched in Python.

In Python (on non-Numpy variables), `~`

means unary complement.
`~`

operates on the bits of the byte underlying each non-Numpy Boolean (in Matlab/Octave, boolean is class `logical`

)

## tl;dr

- Numpy does
*not*allow the word`not`

for Numpy arrays. - safest way (if cumbersome) is to always use
`numpy.logical_not()`

. - If you know you won’t have any Numpy arrays, you can use the word
`not`

. - If you know you
*always*have Numpy arrays, you can use`~`

, but it’s safer to use`numpy.logical_not()`

. `not`

will at least throw a`ValueError`

if you use it on a Numpy array, rather than silently giving the wrong value as`~`

will on non-Numpy arrays.

My operating practice is to use `not`

or `logical_not()`

and avoid `~`

to avoid silent failures.

Type | `~` operation |
---|---|

non-Numpy | unary complement `~False ==- 1; ~True == -2` |

Numpy | logical not `x=numpy.array(False); ~x==True; ~~x==False` |

Matlab | logical not `~false = true; ~true==false` |

This critically important distinction comes from the short int (byte) inherited by the Python `bool`

.

** Tags: **
gnu-octave,
numpy