我如何识别字符串是否应该带参数

Question

I am not sure if there is a pretty way of doing this but here is my problem:

I have a dict that reference to some SQL statements:

{
  'var1': """select * from sometable where x=%s"""
  'var2': """select * from sometable"""
}

I have a script which will either use var1 or var2... but obviously when attempting to pass an argument to var2 it will throw an exception...

I was wondering if there is a way to identify if a string needs an argument and only then try to pass it...

Answer 1

A simple way would be to count the %s strings.

Could fail in some extreme cases, but basically

sql_string.count('%s')

provides you with the number of expected arguments.

d = {
  'var1': """select * from sometable where x=%s""",
  'var2': """select * from sometable"""
}

for k,v in d.items():
    print("{}, {} args".format(k,v.count("%s")))

result:

var2, 0 args
var1, 1 args

had you other formats than %s you could use a regular expression to match other formats, like this:

len(re.findall("%[ds]",sql_string)

Both solutions above are far from perfect. They don't handle % escaping for instance.

Answer 2

Do you mean?

if "%s" in sql_stmt:
    do_something()

Also you can use sql_stmt.count('%s') to get the number of arguments.

Answer 3

dict = {
  "var1": "select * from sometable where x=%s",
  "var2": "select * from sometable"
}
for k,v in dict.iteritems():
    if "%s" in v:
        print "[%s] needs an argument"%v
    else:
        print "[%s] doesn't need an argument"%v

gives :

[select * from sometable where x=%s] needs an argument
[select * from sometable] doesn't need an argument