%precision 2 on Python

问题:

If I have this piece of code:

import csv

%precision 2

with open('blah.csv') as csvfile:
    blah = list(csv.DictReader(csvfile))

What does it means the %precision 2 line?

回答1:

This is an IPython magic. It controls how floats display:

>>> 1.2345
1.2345
>>> %precision 2
'%.2f'
>>> 1.2345
1.23

Documented here.

Note: It suggests your script was intended to be executed within an IPython runtime (such as a notebook). In a regular Python interpreter that will be a syntax error.

回答2:

This is to set a floating point precision for printing. It sets the floating point to 2 decimal points. This doesn't work in all interpreters though, but it does work in Jupyter-Notebook.

NB: Thanks to Chrisz for the point.