This link has been bookmarked by 187 people . It was first bookmarked on 22 Jun 2006, by craig hancock.
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Use function factories to create utility functions. Often, especially if you're using map and filter a lot, you need utility functions that convert other functions or methods to taking a single parameter. In particular, you often want to bind some data to the function once, and then apply it repeatedly to different objects.
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makoto tsuyukiPythonのイディオム
What idioms should I use to make my code easier to read?
Read "The Python Cookbook", especially the first few chapters. It's a great source of well-written Python code examples. -
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result = ''.join(strings)
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for key in d: print key #also works for arbitrary sequence
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if key not in d: d[key] = []
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Note: you still need to use d.keys() if you want to mutate the dictionary. for key in d: del d[key] will raise RuntimeError: dictionary changed size during iteration. Use for key in d.keys(): del d[key] instead.
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use s.startswith('abc') rather than startswith(s, 'abc')
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Use for line in infile, not for line in infile.readlines()
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Worse: #check whether int conversion will raise an error if not isinstance(s, str) or not s.isdigit: return None elif len(s) > 10: #too many digits for int conversion return None else: return int(str) Better: try: return int(str) except (TypeError, ValueError, OverflowError): #int conversion failed return None
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Build strings as a list and use ''.join at the end
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Wrong: for s in strings: result += s Right: result = ''.join(strings)
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Use tests for object identity when appropriate: if x is not None rather than if x != None
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Worse: strings = [] for d in data: strings.append(str(d)) Better: strings = map(str, data)
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Use list comprehensions where there are conditions attached, or where the functions are methods or take more than one parameter
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Use function factories to create utility functions
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def multiply_by_field(fieldname, multiplier): """Returns function that multiplies field "fieldname" by multiplier.""" def multiplier(x): return getattr(x, fieldname) * multiplier return multiplier triple = multiply_by_field('Count', 3) quadruple = multiply_by_field('Count', 4) halve_sum = multiply_by_field('Sum', 0.5)
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Use the operator module and reduce to get sums, products, etc
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Worse: sum = 0 for d in data: sum += d product = 1 for d in data: product *= d Better: from operator import add, mul sum = reduce(add, data) product = reduce(mul, data)
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zarakin nikaraz02-2008: Table of Contents -
- What idioms should I use to make my code easier to read?
- What techniques should I use to make my code run faster?
- Back to the coding guidelines -
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What idioms should I use to make my code easier to read?
Read "The Python Cookbook", especially the first few chapters. It's a great source of well-written Python code examples.
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Use function factories to create utility functions. Often, especially if you're using map and filter a lot, you need utility functions that convert other functions or methods to taking a single parameter. In particular, you often want to bind some data to the function once, and then apply it repeatedly to different objects. In the above example, we needed a function that multiplied a particular field of an object by 3, but what we really want is a factory that's able to return for any field name and amount a multiplier function in that family:
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Use zip and dict to map fields to names. zip turns a pair of sequences into a list of tuples containing the first, second, etc. values from each sequence. For example, zip('abc', [1,2,3]) == [('a',1),('b',2),('c',3)]. You can use this to save a lot of typing when you have fields in a known order that you want to map to names:
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