os is Python’s built-in interface for practical operating-system tasks. It helps programs inspect directories, build filesystem paths, check whether files or folders exist, and create output directories. section 9.5.3 section 9.4.2
Common operations include:
- Use os.listdir(directory) to retrieve the names of files in a directory. section 9.5.3
- Use os.path.join(directory, filename) to construct paths for reading, writing, or comparing files. section 9.4.2 section 9.5.3
- Use os.path.exists(path) to test whether a filename or directory already exists. section 9.5.3 section 9.4.2
- Use os.mkdir(directory) to create a missing output directory. section 9.4.2
Combining picture directories
A duplicate-free picture merger loops through source directories with os.listdir, forms each source path with os.path.join, and compares files before copying them. A filename helper uses os.path.exists to append underscores when a target name is already present. Keeping original directories intact and testing with disposable samples reduces the risk of destructive mistakes. section 9.5.3
Listing 9.5 Improved function to add covers to .pdf documents
import os
import fitz
def add_covers(report_dir, cover_dir, final_dir):
'''
report_dir is a directory of reports named 1.pdf, 2.pdf, and so on.
These files may be one page or more than one page.
cover_dir is a directory of covers, with one cover per report.
The filenames in this directory are cover1.pdf, cover2.pdf, and so on.
Each of these files is one page.
Add the cover to the beginning of each report,
and store all resulting pdfs in final_dir.
'''
if not os.path.exists(final_dir): #1
os.mkdir(final_dir) #2
for report in os.listdir(report_dir): #3
report_path = os.path.join(report_dir, report)
cover_path = os.path.join(cover_dir, f'cover{report}')
final_path = os.path.join(final_dir, report)
cover_doc = fitz.open(cover_path) #4
report_doc = fitz.open(report_path) #5
final_doc = fitz.open() #6
final_doc.insert_pdf(cover_doc) #7
final_doc.insert_pdf(report_doc) #8
final_doc.save(final_path) #9
if __name__ == '__main__':
add_covers('reports', 'covers', 'final')
Browse a complete PDF-cover workflow using os.path.exists, os.mkdir, os.listdir, and os.path.join alongside a document-processing library. section 9.4.2
