Concatenating strings in Python

Question

How can I properly concatenate a variable inside an string in Python?

I am trying to pass service in "Database Connections\\'service'.sde" and (r"C:\GIS\Maps\'.+service+.'.mxd")

service ="Electric"
sde = "Database Connections\\'service'.sde"
mxd = arcpy.mapping.MapDocument(r"C:\GIS\Maps\'.+service+.'.mxd")

so the output looks like

sde = "Database Connections\\Electric.sde"
mxd = arcpy.mapping.MapDocument(r"C:\GIS\Maps\Electric.mxd")

• halfer: If your question was sufficiently answered, you can accept the most helpful answer.

Answer 1

I think a better way to do this is using os.path.join:

import os
mxd = arcpy.mapping.MapDocument(os.path.join(*"C:\\GIS\\Maps\\".split('\\') 
 + ["{}.mxd".format(service)]))

Also, note that your back-slashes need to be escaped.

• Alexander: Aren't you mixing methods? Shouldn't you join each component, e.g. os.path.join(*"C:\\GIS\\Maps\\".split('\\') + ["{}.mxd".format(service)] Surely the `\\` is specific to the operating system, and the point of os.path.join is to join making it OS agnostic.

Answer 2

This is how Python's string concatenation works:

sde = "Database Connections\\" + service + ".sde"
mxd = arcpy.mapping.MapDocument("C:\\GIS\\Maps\\" + service + ".mxd")

• Mona Coder: Thanks Mr Geek but I am getting error on second line!
• Djaouad: @MonaCoder You should escape the ` and remove the r`, check the updated answer.

Answer 3

An alternative which bypasses the issue of raw strings can't end with a single backslash:

r'C:\GIS\Maps\%s.mxd' % service

and

r'C:\GIS\Maps\{}.mxd'.format(service)

both work fine, dodging the issue with the string ending in a backslash.