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Learn Web Development with Python

You're reading from   Learn Web Development with Python Get hands-on with Python Programming and Django web development

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Product type Course
Published in Dec 2018
Publisher
ISBN-13 9781789953299
Length 796 pages
Edition 1st Edition
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Authors (3):
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Fabrizio Romano Fabrizio Romano
Author Profile Icon Fabrizio Romano
Fabrizio Romano
Gaston C. Hillar Gaston C. Hillar
Author Profile Icon Gaston C. Hillar
Gaston C. Hillar
Arun Ravindran Arun Ravindran
Author Profile Icon Arun Ravindran
Arun Ravindran
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Toc

Table of Contents (33) Chapters Close

Title Page
About Packt
Contributors
Preface
1. A Gentle Introduction to Python FREE CHAPTER 2. Built-in Data Types 3. Iterating and Making Decisions 4. Functions, the Building Blocks of Code 5. Saving Time and Memory 6. OOP, Decorators, and Iterators 7. Files and Data Persistence 8. Testing, Profiling, and Dealing with Exceptions 9. Concurrent Execution 10. Debugging and Troubleshooting 11. Installing the Required Software and Tools 12. Working with Models, Migrations, Serialization, and Deserialization 13. Creating API Views 14. Using Generalized Behavior from the APIView Class 15. Understanding and Customizing the Browsable API Feature 16. Using Constraints, Filtering, Searching, Ordering, and Pagination 17. Securing the API with Authentication and Permissions 18. Applying Throttling Rules and Versioning Management 19. Automating Tests 20. Solutions 21. Templates 22. Admin Interface 23. Forms 24. Security 25. Working Asynchronously 26. Creating APIs 27. Production-Ready 1. Other Books You May Enjoy Index

Name localization


Now that we are familiar with all types of comprehensions and generator expression, let's talk about name localization within them. Python 3.* localizes loop variables in all four forms of comprehensions: list, dict, set, and generator expressions. This behavior is therefore different from that of the for loop. Let's see a simple example to show all the cases:

# scopes.py
A = 100
ex1 = [A for A in range(5)]
print(A)  # prints: 100

ex2 = list(A for A in range(5))
print(A)  # prints: 100

ex3 = dict((A, 2 * A) for A in range(5))
print(A)  # prints: 100

ex4 = set(A for A in range(5))
print(A)  # prints: 100

s = 0
for A in range(5):
    s += A
print(A)  # prints: 4

In the preceding code, we declare a global name, A = 100, and then we exercise the four comprehensions: list, generator expression, dictionary, and set. None of them alter the global name, A. Conversely, you can see at the end that the for loop modifies it. The last print statement prints 4.

Let's see what happens...

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