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Super Kai (Kazuya Ito)
Super Kai (Kazuya Ito)

Posted on • Edited on

Positional & Keyword-Only Parameters in Python function

#python #parameter #argument #function

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*Memos:

You can set positional-only parameters and keyword-only parameters together for a function as shown below. */ must be before *:

The parameters without default values: 

def func(fname, /, lname, age, *, gender): pass def func(fname, lname, /, *, age, gender): pass # No error  def func(fname, *, lname, age, /, gender): pass # SyntaxError: / must be ahead of *
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def func(fname, /, lname, age, *, gender): print(fname, lname, age, gender) func("John", "Smith", 36, gender="Male") func("John", "Smith", 36, **{"gender":"Male"}) func("John", lname="Smith", age=36, gender="Male") func("John", **{"lname":"Smith", "age":36, "gender":"Male"}) func("John", "Smith", gender="Male", age=36) func("John", "Smith", **{"gender":"Male", "age":36}) # John Smith 36 Male  func("John", "Smith", 36, "Male") # TypeError: func() takes 3 positional arguments but 4 were given  func(fname="John", lname="Smith", age=36, gender="Male") func(**{"fname":"John", "lname":"Smith", "age":36, "gender":"Male"}) # TypeError: func() got some positional-only arguments passed # as keyword arguments: 'fname'
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def func(fname, lname, /, *, age, gender): print(fname, lname, age, gender) func("John", "Smith", age=36, gender="Male") func("John", "Smith", **{"age":36, "gender":"Male"}) # John Smith 36 Male  func("John", "Smith", 36, "Male") # TypeError: func() takes 2 positional arguments but 4 were given  func(fname="John", lname="Smith", age=36, gender="Male") func(**{"fname":"John", "lname":"Smith", "age":36, "gender":"Male"}) # TypeError: func() got some positional-only arguments passed # as keyword arguments: 'fname, lname'
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The parameters with default values: 

def func(fname="John", /, lname="Smith", age=36, *, gender="Male"): pass def func(fname="John", lname="Smith", /, *, age=36, gender="Male"): pass # No error  def func(fname="John", *, lname="Smith", age=36, /, gender="Male"): pass # SyntaxError: / must be ahead of *
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def func(fname="John", /, lname="Smith", age=36, *, gender="Male"): print(fname, lname, age, gender) func() # John Smith 36 Male  func("Anna", "Brown", 27, gender="Female") func("Anna", "Brown", 27, **{"gender":"Female"}) func("Anna", lname="Brown", age=27, gender="Female") func("Anna", **{"lname":"Brown", "age":27, "gender":"Female"}) func("Anna", age=27, gender="Female", lname="Brown") func("Anna", **{"age":27, "gender":"Female", "lname":"Brown"}) # Anna Brown 27 Female  func("Anna", "Brown", 27, "Female") # TypeError: func() takes from 0 to 3 positional arguments but 4 were given  func(fname="Anna", lname="Brown", age=27, gender="Female") func(**{"fname":"Anna", "lname":"Brown", "age":27, "gender":"Female"}) # TypeError: func() got some positional-only arguments passed # as keyword arguments: 'fname'
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def func(fname="John", lname="Smith", /, *, age=36, gender="Male"): print(fname, lname, age, gender) func("John", "Smith", age=36, gender="Male") func("John", "Smith", **{"age":36, "gender":"Male"}) # John Smith 36 Male  func("John", "Smith", 36, "Male") # TypeError: func() takes from 0 to 2 positional arguments but 4 were given  func(fname="John", lname="Smith", age=36, gender="Male") func(**{"fname":"John", "lname":"Smith", "age":36, "gender":"Male"}) # TypeError: func() got some positional-only arguments passed # as keyword arguments: 'fname, lname'
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