Add solutions to new exercises in section 2

somacdivad · somacdivad · commit 01bb93e3e36a · 2020-01-10T12:09:55.000-06:00
diff --git a/ch13-interact-with-pdf-files/2-extract-pages-from-a-pdf.py b/ch13-interact-with-pdf-files/2-extract-pages-from-a-pdf.py
@@ -1,41 +1,125 @@
 # 13.2 - Extract Pages From a PDF
 # Solutions to review exercises
 
-import os
-import copy
-from pyPDF2 import PdfFileReader, PdfFileWriter
+# ***********
+# Exercise 1
+#
+# Extract the last page from the `Pride_and_Prejudice.pdf` file and
+# save it to a new file called `last_page.pdf` in your home directory.
+# ***********
 
+# First import the classes and libraries needed
+from pathlib import Path
+from PyPDF2 import PdfFileReader, PdfFileWriter
 
-# Exercise 1
-path = "C:/python-basics-exercises/ch13-interact-with-pdf-files/\
-        practice_files"
+# Get the path to the `Pride_and_Prejudice.pdf` file. We'll assume you
+# downloaded the solutions folder and extracted it into the home
+# directory on your computer. If this is not the case, you'll need to
+# update the path below.
+pdf_path = Path.home() / "python-basics-exercises/ch13-interact-with-pdf-files" \
+    "/practice_files/Pride_and_Prejudice.pdf"
+
+# Now you can create the PdfFileReader instance. Remember that
+# PdfFileReader objects can only be instantiated with path strings, not
+# Path objects!
+pdf_reader = PdfFileReader(str(pdf_path))
 
-input_file_path = os.path.join(path, "Walrus.pdf")
-input_file = PdfFileReader(input_file_path)
-output_PDF = PdfFileWriter()
+# Use the .pages attribute to get an iterable over all pages in the
+# PDF. The last page can be accessed with the index -1.
+last_page = pdf_reader.pages[-1]
 
-input_file.decrypt("IamtheWalrus")  # decrypt the input file
+# Now you can create a PdfFileWriter instance and add the last page to it.
+pdf_writer = PdfFileWriter()
+pdf_writer.addPage(last_page)
 
+# Finally, write the contents of pdf_writer to the file `last_page.pdf`
+# in your home directory.
+output_path = Path.home() / "last_page.pdf"
+with output_path.open(mode="wb") as output_file:
+    pdf_writer.write(output_file)
 
+
+# ***********
 # Exercise 2
-for page_num in range(0, input_file.getNumPages()):
-    # rotate pages (call everything page_left for now; will make a copy)
-    page_left = input_file.getPage(page_num)
-    page_left.rotateCounterClockwise(90)
+#
+# Extract all pages with even numbered _indices_ from the
+# `Pride_and_Prejudice.pdf` and save them to a new file called
+# `every_other_page.pdf` in your home directory.
+# ***********
+
+# There are several ways to extract pages with even numbered indices
+# so we'll cover a few of them here.
+
+# Solution A: Using a `for` loop
+# ------------------------------
+
+# One way to do it is with a `for` loop. We'll create a new PdfFileWriter
+# instance, then loop over the numbers 0 up to the number of pages in the
+# PDF, and add the pages with even indices to the PdfFileWriter instance.
+pdf_writer = PdfFileWriter()
+num_pages = pdf_reader.getNumPages()
+
+for idx in range(num_pages):  # NOTE: idx is a common short name for "index"
+    if idx % 2 == 0:  # Check that the index is even
+        page = pdf_reader.getPage(idx)  # Get the page at the index
+        pdf_writer.addPage(page)  # Add the page to `pdf_writer`
+
+# Now write the contents of `pdf_writer` the the file `every_other_page.pdf`
+# in your home directory
+output_path = Path.home() / "every_other_page.pdf"
+with output_path.open(mode="wb") as output_file:
+    pdf_writer.write(output_file)
 
-    page_right = copy.copy(page_left)  # split each page in half
-    upper_right = page_left.mediaBox.upperRight  # get original page corner
+# Solution B: Slicing .`pages` with steps
+# ------------------------------
 
-    # crop and add left-side page
-    page_left.mediaBox.upperRight = (upper_right[0] / 2, upper_right[1])
-    output_PDF.addPage(page_left)
-    # crop and add right-side page
-    page_right.mediaBox.upperLeft = (upper_right[0] / 2, upper_right[1])
-    output_PDF.addPage(page_right)
+# A more succinct, alghouth possibly more difficult to understand,
+# solution involves slicing the `.pages` iterable. The indices start
+# with 0 and every even index can be obtained by iterating over
+# `.pages` in steps of size 2, so `.pages[::2]` is an iterable
+# containing just the pages with even indices.
+pdf_writer = PdfFileWriter()
 
+for page in pdf_reader.pages[::2]:
+    pdf_writer.addPage(page)
 
+# Now write the contents of `pdf_writer` the the file
+# `every_other_page.pdf` in your home directory.
+output_path = Path.home() / "every_other_page.pdf"
+with output_path.open(mode="wb") as output_file:
+    pdf_writer.write(output_file)
+
+
+# ***********
 # Exercise 3
-# save new pages to an output file
-output_file_path = os.path.join(path, "Output/Updated Walrus.pdf")
-with open(output_file_path, "wb") as output_file:
-    output_PDF.write(output_file)
+#
+# Split the `Pride_and_Prejudice.pdf` file into two new PDF files. The
+# first file should contain the first 150 pages, and the second file
+# should contain the remaining pages. Save both files in your home
+# directory as `part_1.pdf` and `part_2.pdf`.
+# ***********
+
+# Start by creating two new PdfFileWriter instances.
+part1_writer = PdfFileWriter()
+part2_writer = PdfFileWriter()
+
+# Next, create two new iterables containing the correct pages.
+part1_pages = pdf_reader.pages[:150]  # Contains pages 0 - 149
+part2_pages = pdf_reader.pages[150:]  # Contains pages 150 - last page
+
+# Add the pages to their corresponding writers.
+for page in part1_pages:
+    part1_writer.addPage(page)
+
+for page in part2_pages:
+    part2_writer.addPage(page)
+
+# Now write the contents of each writer to the files `part_1.pdf` and
+# `part_2.pdf` in your home directory.
+part1_output_path = Path.home() / "part_1.pdf"
+with part1_output_path.open(mode="wb") as part1_output_file:
+    part1_writer.write(part1_output_file)
+
+part2_output_path = Path.home() / "part_2.pdf"
+with part2_output_path.open(mode="wb") as part2_output_file:
+    part2_writer.write(part2_output_file)
