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The 8 Most Common Python Programming Errors

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|  Updated:  
2019-01-27 21:59:07
|   From The Book:  
Python Essentials For Dummies
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Every developer on the planet makes mistakes. However, knowing about common mistakes will save you time and effort later. The following list tells you about the most common errors that developers experience when working with Python:
  • Using the incorrect indentation: Many Python features rely on indentation. For example, when you create a new class, everything in that class is indented under the class declaration. The same is true for decision, loop, and other structural statements. If you find that your code is executing a task when it really shouldn’t be, start reviewing the indentation you’re using.

  • Relying on the assignment operator instead of the equality operator: When performing a comparison between two objects or value, you just use the equality operator (==), not the assignment operator (=). The assignment operator places an object or value within a variable and doesn’t compare anything.

  • Placing function calls in the wrong order when creating complex statements: Python always executes functions from left to right. So the statement MyString.strip().center(21, "*") produces a different result than MyString.center(21, "*").strip(). When you encounter a situation in which the output of a series of concatenated functions is different from what you expected, you need to check function order to ensure that each function is in the correct place.

  • Misplacing punctuation: You can put punctuation in the wrong place and create an entirely different result. Remember that you must include a colon at the end of each structural statement. In addition, the placement of parentheses is critical. For example, (1 + 2) * (3 + 4), 1 + ((2 * 3) + 4), and 1 + (2 * (3 + 4)) all produce different results.

  • Using the incorrect logical operator: Most of the operators don’t present developers with problems, but the logical operators do. Remember to use and to determine when both operands must be True and or when either of the operands can be True.

  • Creating count-by-one errors on loops: Remember that a loop doesn’t count the last number you specify in a range. So, if you specify the range [1:11], you actually get output for values between 1 and 10.

  • Using the wrong capitalization: Python is case sensitive, so MyVar is different from myvar and MYVAR. Always check capitalization when you find that you can’t access a value you expected to access.

  • Making a spelling mistake: Even seasoned developers suffer from spelling errors at times. Ensuring that you use a common approach to naming variables, classes, and functions does help. However, even a consistent naming scheme won’t always prevent you from typing MyVer when you meant to type MyVar.

About This Article

This article is from the book: 

About the book author:

John Paul Mueller is a freelance author and technical editor. He has writing in his blood, having produced 100 books and more than 600 articles to date. The topics range from networking to home security and from database management to heads-down programming. John has provided technical services to both Data Based Advisor and Coast Compute magazines.

Luca Massaron is a data scientist specialized in organizing and interpreting big data and transforming it into smart data by means of the simplest and most effective data mining and machine learning techniques. Because of his job as a quantitative marketing consultant and marketing researcher, he has been involved in quantitative data since 2000 with different clients and in various industries, and is one of the top 10 Kaggle data scientists.