编写Python脚本以使用控制台命令执行

Question

Research is at the bottom, read before -1'ing... Thanks.

I have to write a Python script that runs SQL queries. I made a main class and called SQLQuery. Each SQLQuery instance represents a query. The script must be structured like this:

class SQLQuery(object):

     def __init___(self, string_myQuery)...

instance1 = SQLQuery(SQLQuery1)...

instance2 = SQLQuery(SQLQuery2)...

As a user requirement, the instances must be in the same file as the class (so I can't just make each instance a main and execute that file separately), and each instance must be executed with Linux console commands. I can execute the entire script with a simple python SQLQuery.py but I need to execute each instance separately. The queries will be executed every day, automatically, so I don't need a terminal UI tree. It should be executed with a command similar to this:

python SQLQuery.py -inst1

will execute instance1.

python SQLQuery.py -inst2

will execute instance2.

I have researched how to execute Python scripts with Linux commands and most of the articles are about calling commands from the Python script. However, I found this article from the Python documentation. It suggests adding -m, so:

python SQLQuery.py -m inst1

This would let me set my main with a console command, but it doesn't work since the instances aren't modules. And since the instances must be in the same file as the class, I can't just import them as a module when I execute SQLQuery.py with a console command.

Answer 1

Ignoring all the irrelevancies, it sounds like your problem is that you have a bunch of global objects named instance1 , instance2 , instance3 , etc., and you want to call some method on one of them based on a command-line parameter whose value will be similar to, but not identical to, the instance names.

That's probably not a good idea… but it's not that hard:

if __name__ == '__main__':
    inst = sys.argv[1] # will be 'inst1', 'inst13', etc.
    inst_number = inst[5:] # so '1', '13', etc.
    inst_name = 'instance' + inst_number
    instance = globals()[inst_name]
    instance.execute()

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A much better way to do the same thing is to put the instance globals into a list or dict that you can index.

For example, let's say instead of instance1 , instance2 , etc., you've got an instances dict, with instances['1'] , instances[2] , etc. Now instead of this:

inst_name = 'instance' + inst_number
instance = globals()[inst_name]
instance.execute()

… you just do this:

instances[inst_number].execute()

---

Also, instead of coming up with a command-line parameter that has extra stuff in it that you have to parse and throw away, and has no more meaning for a human reader than for your code, why not just take a number?

python myscript.py 12

Or, alternatively, use argparse to create an argument that can be used in all of the obvious ways:

python myscript.py --instance=12
python myscript.py --instance 12
python myscript.py -i12
python myscript.py -i 12

Either way, your code gets the string '12' , which it can then use to look up the function, as above.

Answer 2

You have the wrong syntax for the -m option. Suppose you have the following file named foo.py :

import sys
print 'First arg is: ', sys.argv[1]

Then you would call it like this:

$ python -m foo bar
First arg is:  bar

Note that the ".py" extension is omitted. You can then use the command line argument to decide which object to use or use the argparse or optparse module to handle the argument.