IPython magic print variables on assignment

Question

Is there a parameter in IPython to print the variables each time I assign them ?

Currently:

In [1]: a = 5

In [2]: a
Out[2]: 5

In [3]: b = a + 1

In [4]: b
Out[4]: 6

In matlab, the variable is printed unless one writes a ; at the end, in ipython I would like to activate this with a magic function like so:

In [1]: %printassignment

In [2]: a = 5
a = 5

In [3]: b = a + 1
b = 6

I could write my own magic, but I'm pretty sure that's something that is so standard people would craft a super tuned, standard, function. The feature is especially useful for beginners.

Answer 1

As of IPython 6.2, this exists, but the command to turn it on is really long:

%config InteractiveShell.ast_node_interactivity='last_expr_or_assign'

You can set it in your ipython_config.py, if you want it to be on by default:

c = get_config()
c.InteractiveShell.ast_node_interactivity = 'last_expr_or_assign'

It only triggers when the assignment target is a simple name; assignments like arr[i] = val or obj.attr = 3 will not auto-print.

Answer 2

Try the following for older versions of IPython…

from IPython.core.inputtransformer import InputTransformer
import re

class PrintAssignment(InputTransformer):
    def __init__(self):
        self.assignment = re.compile('^([a-z]+) =')
        self.most_recent_line = None
    def push(self, line):
        self.most_recent_line = line
        return line
    def reset(self):
        if not self.most_recent_line: return
        match = self.assignment.match(self.most_recent_line)
        self.most_recent_line = None
        if match: return match.group(1)

And then register this input handler with

ip = get_ipython()
ip.physical_line_transforms.append(PrintAssignment())