printing variables values in python. Is there any elegant formatting to do it?

Question

I would like to print variables values in python. e.g:

a=3
b=5
print 'blah blah: a = {a}, b = {b}'.format(a=a, b=b)

result is:

blah blah: a = 3, b = 5

My question is how to do it in a short elegant and readable manner.

e.g., is there a way to write something like (pseudo code below)

print 'blah blah: {a}, {b}'.format(a,b)

to get the same result?

Thanks! (BTW: i am using python 2.7)

EDIT (clarification): For logging purpose, sometimes i have many variables that i would like to print, so i prefer not doing something like

print 'a={}, b={}, c={},...'.format(a,b,c...)

because it is a source for bugs (i.e. I just want to specify the varaible name in the string itself and not care about the order of the variables).

e.g., ultimatly, something that looks like

print 'blah blah: {a}, {b}, {c}, {d}, {e}, {f}'.format(c,e,a,f,d,b)

with a result like:

blah blah: a=3, b=5, c=7, d=22, e=2, f=532

It looks like your problem is that you have to repeat `a` and `b` in `a=a, b=b`? — David Robinson, Sep 18 '14 at 10:39
yes, i find it not elegant to repeat the name of the argument 4 times in order to print its value. — Yuval Atzmon, Sep 18 '14 at 10:41
The problem is that the objects themselves don't know what name[s] they are bound to. If you want something like that you have to use a namespace (i.e. dict). — wim, Sep 18 '14 at 11:00
This reminds me of the MacroPy library, whose [`log`](https://github.com/lihaoyi/macropy#tracing) function seems to do what you want. `log[a]` prints out "a -> 3" (or something similar, I haven't actually tried it myself) — Kevin, Sep 18 '14 at 12:32

score 3 · Accepted Answer · edited Sep 18 '14 at 11:26

3

You can use your second approach with **locals() instead of a, b. locals() returns a dict containing all local variables. ** unpacks it so you can use it in function calls (function(**{'a': 3, 'b': 4, 'c': 14}) is the same as function(a=3, b=4, c=14))

>>> a = 3
>>> b = 4
>>> c = 14
>>> print 'a = {a}, b = {b}'.format(**locals())
a = 3, b = 4

To avoid 'a = {a}' you can do something like

print '{a}, {b}'.format(**{k:'{} = {}'.format(k,v) for (k,v) in locals().iteritems()})

edited Sep 18 '14 at 11:26

Yuval Atzmon

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answered Sep 18 '14 at 10:55

semptic

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Almost perfect! Anyway to shorten it to get the same result? e.g. something like print('{a}, {b}'.format(SOME_MANIPULATION(**locals()))) – Yuval Atzmon Sep 18 '14 at 11:07
Not without creating a function which does this four you (converting `'{a}'` to `'a = {a}'`). – semptic Sep 18 '14 at 11:07
Thanks, I accept your answer, and will add my solution as an edit – Yuval Atzmon Sep 18 '14 at 11:19

score 1 · Answer 2 · edited May 23 '17 at 11:46

1

If you know the order that a and b will be in, you don't need to pass them as named arguments in your formatting:

a = 3
b = 5

print('blah blah: a = {}, b = {}'.format(a, b))

Alternatively you could store your variables in a dictionary as below and then use **kwargs unpacking when passing the dict to format.

d = dict(a=3, b=5)

print('blah blah: a = {a}, b = {a}'.format(**d))

edited May 23 '17 at 11:46

Community

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answered Sep 18 '14 at 10:39

Ffisegydd

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thanks for your answer. yet it is not what i was looking for. see my clarification in the question – Yuval Atzmon Sep 18 '14 at 10:49
I further clarified my question. – Yuval Atzmon Sep 18 '14 at 10:59
He wants the variable name and value to be printed out by putting the value in. – Rob Grant Sep 19 '14 at 10:01

score 0 · Answer 3 · answered Sep 19 '14 at 10:36

import inspect

class fdict(dict):
    def __init__(self, dct):
        for k, v in dct.items():
            self[k] = "{} = {}".format(k, v)

def flocals():
    frame = inspect.currentframe()
    return fdict(frame.f_back.f_locals)

def localformat(string):
    frame = inspect.currentframe()
    dct = fdict(frame.f_back.f_locals)
    return string.format(**dct)

Then import localformat anywhere you want and use this:

>>> a = 5
>>> b = 6
print(localformat('{a}, {b}'))

or call the flocals() to get a string to pass to format.

printing variables values in python. Is there any elegant formatting to do it?

3 Answers3