Printing list, strings and dict within one string using format in Python3.x

Question

I wish to format a string necessary for querying a database as follows:

SELECT "field1", "field2" FROM "measurement" where "status"=0 AND "node"='name1' LIMIT 10

the following comes from a dict:

field1, field2
measurement
node and name1
10

The dict is as follows:

conf = {
  'fields': ['field1', 'field2'],
  'measurement': 'measurement',
  'limit': 10,
  'tags': {'node': 'name1'}
}

I am able to format the string a part of the string (without the tags) as follows:

    QUERY = 'SELECT "{}" FROM {} WHERE "status"=0 LIMIT {}'.format(
             '","'.join(conf['fields'],
             conf['measurement'],
             conf['limit'])

This provides me:

SELECT "field1", "field2" FROM measurement WHERE "status"=0 LIMIT 10

Problem

The key value pair within the tags is in many case dynamic i.e. there is no previously known key (in this example node)

For the string:

QUERY = 'SELECT {} FROM {} WHERE "status"=0 AND "{}"=\'{}\' LIMIT {}

I wish to fill the string format AND "{}"=\'{}\' dynamically (without prior knowledge of the key value pair within tags

How do I achieve this?

I am not sure if:

QUERY = 'SELECT "{}" FROM {} WHERE "status"=0 AND "{}"=\'{}\' LIMIT {}'.format(
                '","'.join(conf['fields']),
                conf['measurement'],
                **conf['tags'],
                conf['limit']
            )

works as it throws the following SyntaxError:

SyntaxError: positional argument follows keyword argument unpacking

The first string you have can only be represented in python if we use """ , since you both have single and double quotes in there, is that correct? also why do you have "node"='name1' and not node=name1 ? — Devesh Kumar Singh
– Devesh Kumar Singh, Commented Jul 21, 2019 at 13:14

Devesh Kumar Singh · Accepted Answer · 2019-07-21 13:29:18Z

1

I have created the formatted string using the dictionary conf['tags'] beforehand to make it easier to apply to QUERY

conf = {
  'fields': ['field1', 'field2'],
  'measurement': 'measurement',
  'limit': 10,
  'tags': {'node': 'name1'}
}

#Create the string using dictionary
dict_str = ''.join('"{}"=\'{}\''.format(key,value) for key, value in conf['tags'].items())

#Create the final format string
QUERY = 'SELECT "{}" FROM "{}" WHERE "status"=0 AND {} LIMIT {}'.format(
                '","'.join(conf['fields']),
                conf['measurement'],
                dict_str,
                conf['limit']
            )
print(QUERY)

The output will be

SELECT "field1","field2" FROM "measurement" WHERE "status"=0 AND "node"='name1' LIMIT 10

answered Jul 21, 2019 at 13:29

Devesh Kumar Singh

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1 Comment

Shan-Desai Over a year ago

works for me! I had a look into the Client Library there might be something in the lines where one makes a generic query of everything and then parse it using the tags dict but your solution is cleaner and easy to work with.

Ido G · Accepted Answer · 2019-07-21 13:40:12Z

0

If you are using python 3.6 and above there is a new way of string formating using f-strings as specified here (python docs). I am not sure I understood your request but that's what I thought you meant:

key = list(conf['tags'].keys())[0]

QUERY = f"""SELECT {conf['fields'][0]}, {conf['fields'][1]} FROM "{conf['measurement']}" WHERE "status"=0 AND "{key}"='{conf['tags'][key]}' LIMIT {conf['limit']}"""

That results in this string:

SELECT "field1", "field2" FROM "measurement" WHERE "status"=0 AND "node"='name1' LIMIT 10

answered Jul 21, 2019 at 13:40

Ido G

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