Blog
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Sorting a Python dict by value with operator.itemgetter
Sorting a Python dict by value? Instead of: Use itemgetter. It’s cleaner AND ~25% faster: Sort by value, then by key:
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Python file modes: Use ‘x’ instead of ‘w’ to avoid overwriting
Write to a file in Python with open(filename, ‘w’). What if filename already exists? Its contents are gone. (I hope you have backups!) Instead, try: If filename already exists, ‘x’ raises an exception. For new files, ‘x’ and ‘w’ are the same.
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Pandas nlargest: Finding top rows faster than sort_values
Retrieve rows of a Python Pandas data frame with the 6 largest values of column x: Even better: Why is it better? On a 3m row, 680 MB data frame, sort/tail took 622 ms. nlargest? Only 84 ms — 7x faster!
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Pandas column arguments: Where one name works, a list does too
A Python Pandas rule of thumb: Wherever you can use a column name (string), you can use multiple column names (a list of strings):
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Pandas sort_values: Sorting a data frame by multiple columns
To sort a Python Pandas data frame by column x: By x and y (ascending): By x and y, both descending: Ascending x, descending y:
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Pandas select_dtypes: Selecting columns by their dtype
Need specific column types in Python Pandas? Use select_dtypes:
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Python line continuation: How parentheses split long lines
Use parentheses to split long Python code across lines: But with parentheses, Python sees it as one line: Or in comprehensions…
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Jupyter memory usage: Why del doesn’t free your DataFrame
Python Jupyter memory quirk: Deleting variables doesn’t always free memory! Use df.head() instead of df to keep big values out of Jupyter’s Out dict.
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Python set subset checks with <=: Spelling Bee word validation
Playing NYT Spelling Bee? Use Python to see if your word only uses allowed letters (ignoring length + center): With sets, <= checks “subset or equal”: