Python: How to append file content into format string?

Question

I am trying to insert the file content of an multi-line SQL file within a Python script:

sql_file = open(sql_file_path, 'r')
file_content = sql_file.read()
file_content = file_content.replace("placeholder", "realvalue")

import_cmd = 'ogr2ogr -f "PostgreSQL" \
-lco GEOMETRY_NAME=the_geom \
PG:"host=localhost user={db_user_name} port=5432 \
dbname={db_name} password={db_password}" \
{source_file} -nln "{db_table_name}" \
-sql "$(cat {file_content})"'

os.system(import_cmd.format(
  db_user_name=db_user_name,
  db_name=db_name,
  db_password=db_password,
  source_file=source_file,
  db_table_name=db_table_name,
  file_content=file_content
))

The file sql_file_path contains multiple lines. The content is modified via replace. Then th new file_content has to be appended to the -sql parameter of the ogr2ogr command line tool. However, the script throws this error:

Syntax error: "(" unexpected (expecting ")")

did you really want to "$(cat {file_content})" and not echo? — Dinesh
– Dinesh, Commented Oct 21, 2014 at 22:53

Martijn Pieters · Accepted Answer · 2014-10-21 22:10:54Z

1

Don't use os.system. Use subprocess.call() and pass in your arguments as a list:

import subprocess

conn_info = (
    'PG:host=localhost user={db_user_name} port=5432 '
    'dbname={db_name} password={db_password}'.format(
        db_user_name=db_user_name,
        db_name=db_name,
        db_password=db_password))

subprocess.call([
    'ogr2ogr', '-f', 'PostgreSQL', '-lco', 'GEOMETRY_NAME=the_geom',
    conn_info, source_file, '-nln', db_table_name, '-sql', file_content])

This won't go through a shell but invokes the program directly, and each argument passed in directly as is. No further quoting required.

edited Oct 21, 2014 at 22:10

answered Oct 21, 2014 at 21:59

Martijn Pieters

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2 Comments

JJD Over a year ago

The process fails with : File name too long when I pass the multi-line file_content.

Martijn Pieters Over a year ago

@JJD: are you certain that the order of arguments works for the tool? The documentation is a little cryptic, but perhaps the -sql parameter has to come before the the dst_datasource_name and src_datasource_name arguments. What does a working command line (with quotes) look like?

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