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

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Iterable unpacking in Python variable assignment

#python #iterableunpacking #variable #assignment

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*Memos:

  • My post explains variable assignment.
  • My post explains * for iterable unpacking in variable assignment.
  • My post explains * for iterable unpacking in function.
  • My post explains ** for dictionary unpacking.
  • My post explains *args and **kwargs in function.

You can unpack the iterable which has zero or more values to one or more variables as shown below:

*Memos:

  • A set of the one or more variables with one or more commas(,) in a variable assignment is an iterable unpacking so v1 = and v1, = are different.
  • The number of variables must match the number of values unless a *variable is used.
  • The one or more values with one or more commas(,) are a tuple. 
v1, v2, v3 = [0, 1, 2] v1, v2, v3 = 0, 1, 2 # Tuple v1, v2, v3 = (0, 1, 2) # No error  v1, v2, v3 = [0, 1] # ValueError: not enough values to unpack (expected 3, got 2)  v1, v2, v3 = [0, 1, 2, 3] # ValueError: too many values to unpack (expected 3)
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v1 = [0, 1, 2] # It's not an iterable unpacking. # No error  v1, = [0, 1, 2] # ValueError: too many values to unpack (expected 1)
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*Again, a set of the one or more variables with one or more commas(,) in a variable assignment is an iterable unpacking.

v1, = [5] v1, = 5, # Tuple v1, = (5,) v1, = 5 # TypeError: cannot unpack non-iterable int object  v1, = [5, 10] # ValueError: too many values to unpack (expected 1)  v1, = [] # ValueError: not enough values to unpack (expected 1, got 0)  , = [] # SyntaxError: invalid syntax  _, = [] # ValueError: not enough values to unpack (expected 1, got 0)
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v1, v2, v3 = [0, 1, 2] v1, v2, v3 = 0, 1, 2 # Tuple v1, v2, v3 = (0, 1, 2) v1, v2, v3 = range(3) print(v1, v2, v3) # 0 1 2
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v1 = [0, 1, 2] # It's not an iterable unpacking.  print(v1) # [0, 1, 2]
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v1, = [5] v1, = 5, # Tuple v1, = (5,) v1, = range(5, 6) print(v1) 5
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By default, one or more keys can be assigned to one or more variables from a dictrionary same as using keys() as shown below:

v1, v2, v3 = {"name":"John", "age":36, "gender":"Male"} v1, v2, v3 = {"name":"John", "age":36, "gender":"Male"}.keys() print(v1, v2, v3) # name age gender
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One or more values can be assigned to one or more variables from a dictionary with values() as shown below:

v1, v2, v3 = {"name":"John", "age":36, "gender":"Male"}.values() print(v1, v2, v3) # John 36 Male
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One or more keys and values can be assigned to one or more variables from a dictionary with items() as shown below:

v1, v2, v3 = {"name":"John", "age":36, "gender":"Male"}.items() print(v1, v2, v3) # ('name', 'John') ('age', 36) ('gender', 'Male')  print(v1[0], v1[1], v2[0], v2[1], v3[0], v3[1]) # name John age 36 gender Male
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One or more characters can be assigned to one or more variables from a string as shown below:

v1, v2, v3, v4, v5 = "Hello" print(v1, v2, v3, v4, v5) # H e l l o
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