Array column separations for beginners

[Peter Otten]

katarin.bern at gmail.com wrote:

> Hi again,
> 
> I am trying to subtract the minimum value from all numbers (in one array).
> I am using this:
> 
> 
> (array[:,1] -= np.min(array[:,1])   but I alsways have syntaxerror:invalid
> syntax. Do I need some import for this -=? or its something else? THanks!

The name np is probably a reference to numpy, so you need an import for it:

import numpy as np

However, when you forget the above import you will get a NameError like

>>> np
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'np' is not defined

whereas a SyntaxError indicates that your code is not valid Python. The 
problem are the surrounding parentheses. A simple example:

>>> x = 42

Wrong:

>>> (x -= 1)
  File "<stdin>", line 1
    (x -= 1)
        ^
SyntaxError: invalid syntax

Correct:

>>> x -= 1
>>> x
41