string - Variable interpolation in Python

10
votes

Possible Duplicate:
Unpythonic way of printing variables in Python?

In PHP one can write:

$fruit = 'Pear';
print("Hey, $fruit!");

But in Python it's:

fruit = 'Pear'
print("Hey, {0}!".format(fruit))

Is there a way for me to interpolate variables in strings instead? And if not, how is this more pythonic?

Bonus points for anyone who gets the reference

5
pythonstring
All the existing answers are (severely) obsolete as of Python 3.x and in particular 3.6. With f-strings in 3.6 we can now do print(f'Hey, {fruit}!') And much more (all the formatting operators, access list elements and attributes, call str() or repr() with !s or !r ... - smci

5 Answers

7
votes

The way you're doing it now is a pythonic way to do it. You can also use the locals dictionary. Like so:

>>> fruit = 'Pear'
>>> print("Hey, {fruit}".format(**locals()))
Hey, Pear

Now that doesn't look very pythonic, but it's the only way to achieve the same affect you have in your PHP formatting. I'd just stick to the way you're doing it.

12
votes

The closest you can get to the PHP behaviour is and still maintaining your Python-zen is:

print "Hey", fruit, "!"

print will insert spaces at every comma.

The more common Python idiom is:

print "Hey %s!" % fruit

If you have tons of arguments and want to name them, you can use a dict:

print "Hey %(crowd)s! Would you like some %(fruit)s?" % { 'crowd': 'World', 'fruit': 'Pear' }
2
votes

A slight adaptation from the NamespaceFormatter example in PEP-3101:

import string

class NamespaceFormatter(string.Formatter):
  def __init__(self, namespace={}):
      super(NamespaceFormatter, self).__init__()
      self.namespace = namespace

  def get_value(self, key, args, kwds):
      if isinstance(key, str):
          try:
              # Check explicitly passed arguments first
              return kwds[key]
          except KeyError:
              return self.namespace[key]
      else:
          super(NamespaceFormatter, self).get_value(key, args, kwds)

fmt = NamespaceFormatter(globals())
fruit = 'Pear'

print fmt.format('Hey, {fruit}!')

for:

Hey, Pear!
1
votes

Something like this should work:

"%(fruit)s" % locals()
-3
votes

Don't do it. It is unpythonic. As example, when you add translations to your app, you can't longer control which variables are used unless you check all the translations files yourself.

As example, if you change a local variable, you'll have to change it in all translated strings too.