Is it possible to generate and execute Python code in a Python script? [Dynamic Python code]

Question

I am working on some reports (counts) and I have to fetch counts for different parameters. Pretty simple but tedious.

A sample query for one parameter :

qCountsEmployee = (
    "select count(*) from %s where EmployeeName is not null"
     % (tablename)
     )
CountsEmployee = execute_query(qCountsEmployee)

Now I have few hundred such parameters!

What I did was : create a list of all the parameters and generate them using a quick Python script and then copy that text and put it in the main script to avoid the tedious lines.

columnList = ['a', 'b', ............'zzzz']

for each in columnList:
   print (
            'q' + each + ' ='
            + '"select count(*) from %s where' + each
            + 'is not null" % (tablename)'
         )
   print each + '   = execute_query(' + 'q' + each + ')'

While this approach works, I was wondering if instead of a separate script to generate lines of code and copy paste into main program, can I generate them in the main script directly and let the script treat them as lines of code? That will make the code much more readable is what I think. Hope I made sense! Thank you...

Ethan Furman · Accepted Answer · 2011-11-22 21:20:37Z

5

It would be possible, but is not useful here.

Just do something like

columnList = ['a', 'b', ............'zzzz']

results = {}
for column in columnList:
    query = (
            "select count(*) from " + tablename
            + " where " + column + " is not null"
            )
    result = execute_query(qCountsEmployee)
    results[column] = result

You as well can put all this together in a generator function and do

def do_counting(column_list):
    for column in column_list:
        query = (
            "select count(*) from " + tablename
            + " where " + column + " is not null"
            )
        result = execute_query(qCountsEmployee)
        yield column, result

result_dict = dict(do_counting(['...']))

edited Nov 22, 2011 at 21:20

Ethan Furman

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answered Nov 22, 2011 at 18:00

glglgl

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2 Comments

ThinkCode Over a year ago

Can you please explain your generator solution?

glglgl Over a year ago

It iterates over the contents of the given list and yields a 2-tuple for each item. These 2-tuples are then put together into a dict.

William Pursell · Accepted Answer · 2011-11-22 18:01:32Z

2

You can do:

cmd = compile( 'a = 5', '<string>', 'exec' )
exec( cmd )

That is the same as just writing:

a = 5

The string passed as the first argument to compile can be built dynamically.

answered Nov 22, 2011 at 18:01

William Pursell

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3 Comments

ThinkCode Over a year ago

While I love the one-liner (or 2), applying this to my query and quotes is kinda confusing. Will try and let you know if it works. Thanks!

Dave Over a year ago

Go ahead and try it, but exec() is evil. You should do as glglgl suggests and write a program that does what you want without dynamic code.

ThinkCode Over a year ago

Thank you, I take your exec is evil suggestion!

TimothyAWiseman · Accepted Answer · 2011-11-22 22:27:45Z

2

To build on what glglgl said, you are probably better with dynamic SQL than dynamic Python (though Dynamic Python is definitely possible using things like eval ). When working with Dynamic SQL, you should be careful of sql injection. It seems like it would not come up in your particular use-case, but it certainly comes up more often than many developers realize.

I happen to have written an article about SQL Injection and Python which is available at Simple-talk.

edited Nov 22, 2011 at 22:27

answered Nov 22, 2011 at 18:16

TimothyAWiseman

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