Arrays: Difference between revisions
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m →{{header|Python}}: Correct mix-up of mutables/immutables |
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<lang python>myArray = [[0]* width] * height] # DOES NOT WORK AS INTENDED!!!</lang> |
<lang python>myArray = [[0]* width] * height] # DOES NOT WORK AS INTENDED!!!</lang> |
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This creates a list of "height" number of references to one list object ... which is a list of width instances of the number zero. Due to the differing semantics of |
This creates a list of "height" number of references to one list object ... which is a list of width instances of the number zero. Due to the differing semantics of immutables (strings, numbers) and mutables (dictionaries, lists), a change to any one of the "rows" will affect the values in all of them. Thus we need to ensure that we initialize each row with a newly generated list. |
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To initialize a list of lists one could use a pair of nested list comprehensions like so: |
To initialize a list of lists one could use a pair of nested list comprehensions like so: |
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