GStrings in Python

Question

Groovy has a concept of GStrings. I can write code like this:

def greeting = 'Hello World'
println """This is my first program ${greeting}"""

I can access the value of a variable from within the String.

How can I do this in Python?

-- Thanks

Answer 1

d = {'greeting': 'Hello World'}
print "This is my first program %(greeting)s" % d

Answer 2

You can't exactly...

I think the closest you can really get is using standard %-based substitution, e.g:

greeting = "Hello World"
print "This is my first program %s" % greeting

Having said that, there are some fancy new classes as of Python 2.6 which can do this in different ways: check out the string documentation for 2.6, specifically from section 8.1.2 onwards to find out more.

Answer 3

If your trying to do templating you might want to look into Cheetah. It lets you do exactly what your talking about, same syntax and all.

http://www.cheetahtemplate.org/

Answer 4

In Python 2.6+ you can do:

"My name is {0}".format('Fred')

Check out PEP 3101.

Answer 5

In Python, you have to explicitely pass a dictionary of possible variables, you cannot access arbitrary "outside" variables from within a string. But, you can use the locals() function that returns a dictionary with all variables of the local scope.

For the actual replacement, there are many ways to do it (how unpythonic!):

greeting = "Hello World"

# Use this in versions prior to 2.6:
print("My first programm; %(greeting)s" % locals())

# Since Python 2.6, the recommended example is:
print("My first program; {greeting}".format(**locals()))

# Works in 2.x and 3.x:
from string import Template
print(Template("My first programm; $greeting").substitute(locals()))