Does Python do variable interpolation similar to “string #{var}” in Ruby?

Question

In Python, it is tedious to write:

print \"foo is\" + bar + \'.\'

Can I do something like this in Python?

print \"foo is #{ba

Answer 1

I prefer this approach because you don't have to repeat yourself by referencing the variable twice:

alpha = 123
print 'The answer is {alpha}'.format(**locals())

Answer 2

Almost every other answer didn't work for me. Probably it's because I'm on Python3.5. The only thing which worked is:

 print("Foobar is %s%s" %('Foo','bar',))

Answer 3

Python 3.6+ does have variable interpolation - prepend an f to your string:

f"foo is {bar}"

For versions of Python below this (Python 2 - 3.5) you can use str.format to pass in variables:

# Rather than this:
print("foo is #{bar}")

# You would do this:
print("foo is {}".format(bar))

# Or this:
print("foo is {bar}".format(bar=bar))

# Or this:
print("foo is %s" % (bar, ))

# Or even this:
print("foo is %(bar)s" % {"bar": bar})

Answer 4

Python 3.6 will have has literal string interpolation using f-strings:

print(f"foo is {bar}.")

Answer 5

There is a big difference between this in Ruby:

print "foo is #{bar}."

And these in Python:

print "foo is {bar}".format(bar=bar)

In the Ruby example, bar is evaluated
In the Python example, bar is just a key to the dictionary

In the case that you are just using variables the behave more or less the same, but in general, converting Ruby to Python isn't quite so simple

Answer 6

I have learned the following technique from Python Essential Reference:

>>> bar = "baz"
>>> print "foo is {bar}.".format(**vars())
foo is baz.

This is quite useful when we want to refer to many variables in the formatting string:

• We don't have to repeat all variables in the argument list again: compare it to the explicit keyword argument-based approaches (such as "{x}{y}".format(x=x, y=y) and "%(x)%(y)" % {"x": x, "y": y}).
• We don't have to check one by one if the order of variables in the argument list is consistent with their order in the formatting string: compare it to the positional argument-based approaches (such as "{}{}".format(x, y), "{0}{1}".format(x, y) and "%s%s" % (x, y)).