I'm using the troposhere library and I'm trying to combine two string objects which have Join:

from troposphere import Join

str1 = Join('', ["""
sed -i -e '/hostname/s/=.*/=example.com/' /tmp/file.app
\n"""])

and

str2 = Join('', ["""
sed -i -e '/IP/s/=.*/=192.168.100.100/' /tmp/file.app
\n"""])

I've tried to combine them using:

str3 = str1 + str2
and
str1 += str2

But unfortunately I'm getting the following error:

TypeError: unsupported operand type(s) for +: 'Join' and 'Join'

Use string concatenation before Join :

You could just apply string concatenation before creating Joins :

from troposphere import Join

str1 = """
sed -i -e '/hostname/s/=.*/=example.com/' /tmp/file.app
\n"""

str2 = """
sed -i -e '/IP/s/=.*/=192.168.100.100/' /tmp/file.app
\n"""

str3 = str1.strip()+str2

join1, join2, join3 = [Join('', [cmd]) for cmd in (str1, str2, str3)]

print join3.data
# {'Fn::Join': ['', ["sed -i -e '/hostname/s/=.*/=example.com/' /tmp/file.app\nsed -i -e '/IP/s/=.*/=192.168.100.100/' /tmp/file.app\n\n"]]}

Define Join addition :

Here's the definition of Join class :

class Join(AWSHelperFn):
    def __init__(self, delimiter, values):
        validate_delimiter(delimiter)
        self.data = {'Fn::Join': [delimiter, values]}

To define join_a + join_b, you could use :

from troposphere import Join


def add_joins(join_a, join_b):
    delimiter = join_a.data['Fn::Join'][0]
    str_a = join_a.data['Fn::Join'][1][0]
    str_b = join_b.data['Fn::Join'][1][0]

    return Join(delimiter, [str_a.strip() + str_b])

Join.__add__ = add_joins

str1 = """
sed -i -e '/hostname/s/=.*/=example.com/' /tmp/file.app
\n"""

str2 = """
sed -i -e '/IP/s/=.*/=192.168.100.100/' /tmp/file.app
\n"""

join1 = Join('', [str1])
join2 = Join('', [str2])

print (join1 + join2).data
# {'Fn::Join': ['', ["sed -i -e '/hostname/s/=.*/=example.com/' /tmp/file.app\nsed -i -e '/IP/s/=.*/=192.168.100.100/' /tmp/file.app\n\n"]]}