Monthly Archives: December 2017

How to sort a dictionary by values in Python

By definition, dictionary are not sorted (to speed up access). Let us consider the following dictionary, which stores the age of several persons as values: d = {"Pierre": 42, "Anne": 33, "Zoe": 24}d = {"Pierre": 42, "Anne": 33, "Zoe": 24} … Continue reading

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Python: how to copy a list

To explain how to create a copy of a list, let us first create a list. We will use a simple list of 4 items: list1 = [1, 2, "a", "b"]list1 = [1, 2, "a", "b"] Why do we want … Continue reading

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Python: ternary operator

In C language (and many other languages), there is a compact ternary conditional operator that is a compact if-else conditional construct. For instance, in C, a traditional if-else construct looks like: if (a > b) { result = x; } … Continue reading

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Difference between __repr__ and __str__ in Python

When implementing a class in Python, you usually implement the __repr__ and __str__ methods. __str__ should print a readable message __repr__ should print a message that is unambigous (e.g. name of an identifier, class name, etc). You can see __str__ … Continue reading

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python: how to merge two dictionaries

Let us suppose two dictionaries storing ages of different individuals: list1 = {"Pierre": 28, "Jeanne": 27} list2 = {"Marc": 32, "Helene": 34}list1 = {"Pierre": 28, "Jeanne": 27} list2 = {"Marc": 32, "Helene": 34} If you do mind losing the contents … Continue reading

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Search for a pattern in a set of files using find and grep commands

A common task for developers is to search for a pattern amongst a bunch of files that are in different directories. For instance, you are looking for the pattern “import sys” within a set of Python files. Those files are … Continue reading

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