ScraperWiki Python library

This is a Python library for scraping web pages and saving data. It is the easiest way to save data on the ScraperWiki platform, and it can also be used locally or on your own servers.

Installing

pip install scraperwiki

Scraping

scraperwiki.scrape(url[, params][,user_agent])

Returns the downloaded string from the given url.

params are sent as a POST if set.

user_agent sets the user-agent string if provided.

Saving data

Helper functions for saving and querying an SQL database. Updates the schema automatically according to the data you save.

Currently only supports SQLite. It will make a local SQLite database. It is based on SQLAlchemy. You should expect it to support other SQL databases at a later date.

scraperwiki.sql.save(unique_keys, data[, table_name="swdata"])

Saves a data record into the datastore into the table given by table_name.

data is a dict object with field names as keys; unique_keys is a subset of data.keys() which determines when a record is overwritten. For large numbers of records data can be a list of dicts.

scraperwiki.sql.save is entitled to buffer an arbitrary number of rows until the next read via the ScraperWiki API, an exception is hit, or until process exit. An effort is made to do a timely periodic flush. Records can be lost if the process experiences a hard-crash, power outage or SIGKILL due to high memory usage during an out-of-memory condition. The buffer can be manually flushed with scraperwiki.sql.flush().

scraperwiki.sql.execute(sql[, vars])

Executes any arbitrary SQL command. For example CREATE, DELETE, INSERT or DROP.

vars is an optional list of parameters, inserted when the SQL command contains ‘?’s. For example:

scraperwiki.sql.execute("INSERT INTO swdata VALUES (?,?,?)", [a,b,c])

The ‘?’ convention is like "paramstyle qmark" from Python's DB API 2.0 (but note that the API to the datastore is nothing like Python's DB API). In particular the ‘?’ does not itself need quoting, and can in general only be used where a literal would appear. (Note that you cannot substitute in, for example, table or column names.)

scraperwiki.sql.select(sqlfrag[, vars])

Executes a select command on the datastore. For example:

scraperwiki.sql.select("* FROM swdata LIMIT 10")

Returns a list of dicts that have been selected.

vars is an optional list of parameters, inserted when the select command contains ‘?’s. This is like the feature in the .execute command, above.

scraperwiki.sql.commit()

Commits to the file after a series of execute commands. (sql.save auto-commits after every action).

scraperwiki.sql.show_tables([dbname])

Returns an array of tables and their schemas in the current database.

scraperwiki.sql.table_info(name)

Returns an array of attributes for each element of the table.

scraperwiki.sql.save_var(key, value)

Saves an arbitrary single-value into a table called swvariables. Intended to store scraper state so that a scraper can continue after an interruption.

scraperwiki.sql.get_var(key[, default])

Retrieves a single value that was saved by save_var. Only works for string, float, or int types. For anything else, use the pickle library to turn it into a string.

Miscellaneous

scraperwiki.status(type, message=None)

If run on the ScraperWiki platform (the new one, not Classic), updates the visible status of the dataset. If not on the platform, does nothing. type can be 'ok' or 'error'. If no message is given, it will show the time since the update. See dataset status API in the documentation for details.

scraperwiki.pdftoxml(pdfdata)

Convert a byte string containing a PDF file into an XML file containing the coordinates and font of each text string (see the pdftohtml documentation for details). This requires pdftohtml which is part of poppler-utils.

Environment Variables

SCRAPERWIKI_DATABASE_NAME

default: scraperwiki.sqlite - name of database

SCRAPERWIKI_DATABASE_TIMEOUT

default: 300 - number of seconds database will wait for a lock