Merge pull request #216 from anakin87/master

Add faq section

docs/index.rst

@@ -109,6 +109,7 @@ This part of the documentation begins with some background information about why
    user/install
    user/how-it-works
    user/quickstart
+   user/faq
    user/advanced
    user/cli
 

docs/user/faq.rst

@@ -0,0 +1,51 @@
+.. _faq:
+
+Frequently Asked Questions
+==========================
+
+This part of the documentation answers some common questions. To add questions, please open an issue `here <https://github.com/camelot-dev/camelot/issues/new>`_.
+
+How to reduce memory usage for long PDFs?
+-----------------------------------------
+
+During table extraction from long PDF documents, RAM usage can grow significantly.
+
+A simple workaround is to divide the extraction into chunks, and save extracted data to disk at the end of every chunk.
+
+For more details, check out this code snippet from `@anakin87 <https://github.com/anakin87>`_:
+
+::
+
+    import camelot
+
+
+    def chunks(l, n):
+        """Yield successive n-sized chunks from l."""
+        for i in range(0, len(l), n):
+            yield l[i : i + n]
+
+
+    def extract_tables(filepath, pages, chunks=50, export_path=".", params={}):
+        """
+        Divide the extraction work into n chunks. At the end of every chunk,
+        save data on disk and free RAM.
+
+        filepath : str
+            Filepath or URL of the PDF file.
+        pages : str, optional (default: '1')
+            Comma-separated page numbers.
+            Example: '1,3,4' or '1,4-end' or 'all'.
+        """
+
+        # get list of pages from camelot.handlers.PDFHandler
+        handler = camelot.handlers.PDFHandler(filepath)
+        page_list = handler._get_pages(filepath, pages=pages)
+
+        # chunk pages list
+        page_chunks = list(chunks(page_list, chunks))
+
+        # extraction and export
+        for chunk in page_chunks:
+            pages_string = str(chunk).replace("[", "").replace("]", "")
+            tables = camelot.read_pdf(filepath, pages=pages_string, **params)
+            tables.export(f"{export_path}/tables.csv")