Python.md

Table of Contents

• Python
  • Unexpected and surprising
    • Default variables and references

Python

Unexpected and surprising

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Default variables and references

def foo(a=[]):
    a.append(5)
    return a

print(foo())
print(foo())

Expected result: [5] and [5]

Result: [5] and [5,5]

Reason: default arguments are passed by reference, so if changed, the default argument also changes.

Tested with: Python 2.7, Python 3.6

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