CODEWITHSUNDEEP
pythonpython-2.7
Mysteri0n
Mysteri0n

Reputation: 167

Concatenate String With Ternary Operator

I'm trying to dynamically add some additional strings to a query if a file exists that a table is created from. The end ternary works if I remove the first one. I get a syntax error when trying to print out the string below. 

testQuery = """
select 
fish,
"""+("""Room,""" if os.path.isfile(schoolFile)==True else """""")+
"""period_01,
period_02

from over_cs_doe d
"""+("""LEFT JOIN schools s ON s.fish=d.fish""" if os.path.isfile(schoolFile)==True else """""")

Upvotes: 0

Views: 3100

Answers (4)

Davos
Davos

Reputation: 5415

For Python 3.6 onward I would use f-strings, no need to worry about line continuation or positional interpolation like the %s placehholders.

For example:

is_school_file = os.path.isfile(schoolFile)
testQuery = f"""
select 
  fish,
{"  room," if is_school_file else ""}
  period_01,
  period_02
from over_cs_doe as d
{"left join schools as s ON s.fish=d.fish" if is_school_file else ""}"""

If you are using a DB-API compliant database library, or and ORM like SQLAlchemy then there are safer ways to contruct queries that avoid SQL injection. This doesn't look like a case where there might be any unsanitized user-input, but it is responsible to mention it wherever people are concatenating strings to create SQL statements, because SQL Injection is still the #1 code vulnerability.

Upvotes: 0

Mr. E
Mr. E

Reputation: 2120

Your code is almost ok, the problem is that you must use \ at the end of the line if you intend to continue you statement in the next line

testQuery = """
select 
fish,
"""+("""Room,""" if os.path.isfile(schoolFile) else """""") + \ #Use backslash to continue your statement
"""period_01,
period_02

from over_cs_doe d
"""+("""LEFT JOIN schools s ON s.fish=d.fish""" if os.path.isfile(schoolFile) else """""")

Also as I said in a comment, don't test if a boolean values is true

Upvotes: 3

manu190466
manu190466

Reputation: 1603

You can mix strings and code this way but it's not easy to read. Why not trying something like :

if os.path.isfile(schoolFile):
   testQuery = """
   select Fish,Room,period_01 ...
   from ...
"""

else:
   testQuery = """
   select Fish,period_01 ...
   from ...
"""

Upvotes: 0

sebastian
sebastian

Reputation: 9696

For what it's worth, a much more readable and less error prone alternative would be using string interpolation rather than concatenation.

Plus, as the comments suggest, 'something == True' in a "boolean" manner is certainly not considered good style. The same applies to using triple-quoted strings where they aren't needed.

So, your testQuery could also look like:

testQuery = """
select
fish,
%s
period_01,
period_02

from over_cs_doe d
%s
""" % ("Room," if os.path.isfile(schoolFile) else "",
       "LEFT JOIN schools s ON s.fish=d.fish" if os.path.isfile(schoolFile) else "")

Upvotes: 0

Related Questions