diff --git a/.gitignore b/.gitignore
index e10ba39e8..1c19995a8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,7 +8,7 @@
 *.orig
 *.tmp
 
-
+*.idea
 # #########################################################
 # Global/Diff.gitignore
 # #####################################
diff --git a/books/free-programming-books-langs.md b/books/free-programming-books-langs.md
index acd4aad7c..c3d4fafb4 100644
--- a/books/free-programming-books-langs.md
+++ b/books/free-programming-books-langs.md
@@ -1990,7 +1990,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Automate the Boring Stuff with Python, 3nd Edition: Practical Programming for Total Beginners](https://automatetheboringstuff.com/3e/) - Al Sweigart (HTML) (CC BY-NC-SA)
 * [Beej's Guide to Python Programming - For Beginners](http://beej.us/guide/bgpython/) - Brian "Beej Jorgensen" Hall (HTML,PDF)
 * [Beyond the Basic Stuff with Python](https://inventwithpython.com/beyond/) - Al Sweigart (3.x)
-* [Biopython Tutorial and Cookbook](https://biopython.org/DIST/docs/tutorial/Tutorial.pdf) (PDF)
+* [Biopython Tutorial and Cookbook](https://biopython.org/wiki/Documentation) (HTML, PDF) 
 * [Build applications in Python the antitextbook](http://github.com/thewhitetulip/build-app-with-python-antitextbook) (3.x) (HTML, PDF, EPUB, Mobi)
 * [Building Data Products: The Ultimate Guide](https://resources.montecarlodata.com/c/ebook-building-data-products?x=gEwOdf) (HTML, EPUB)
 * [Building Skills in Object-Oriented Design, V4](https://slott56.github.io/building-skills-oo-design-book/build/html/) - Steven F. Lott (3.7)
diff --git a/books/free-programming-books-subjects.md b/books/free-programming-books-subjects.md
index 7f9decda3..87752656e 100644
--- a/books/free-programming-books-subjects.md
+++ b/books/free-programming-books-subjects.md
@@ -301,6 +301,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Introduction to Data Science in Python](https://www.coursera.org/learn/python-data-analysis) - Christopher Brooks (University of Michigan) (Coursera)
 * [Julia Data Science](https://juliadatascience.io) - Jose Storopoli, Rik Huijzer, Lazaro Alonso (HTML) (CC BY-NC-SA 4.0)
 * [Mining of Massive Datasets](http://infolab.stanford.edu/~ullman/mmds/book.pdf) - Jure Leskovec, Anand Rajaraman, Jeffrey D. Ullman (PDF)
+* [Principles of Data Science](https://openstax.org/details/books/principles-data-science) - OpenStax (HTML, PDF) Shaun V. Ault (CC BY-NC-SA 4.0)
 * [Probability and Statistics with Examples using R](https://www.isibang.ac.in/~athreya/psweur/index.html#usage) - Siva Athreya, Deepayan Sarkar, Steve Tanner (HTML) *( :construction: *in process*)*
 * [Python for Data Science – Hands-on Projects](https://www.youtube.com/watch?v=vaMMLLf0wLM) - LunarTech (freeCodeCamp) (YouTube)
 * [School of Data Handbook](https://schoolofdata.org/handbook/)