Python: Builds a list, using an iterator function and an initial seed value

Python List: Exercise - 219 with Solution

Write a Python program to build a list, using an iterator function and an initial seed value.

  • The iterator function accepts one argument (seed) and must always return a list with two elements ([value, nextSeed]) or False to terminate.
  • Use a generator function, fn_generator, that uses a while loop to call the iterator function and yield the value until it returns False.
  • Use a list comprehension to return the list that is produced by the generator, using the iterator function.

Sample Solution:

Python Code:

def unfold(fn, seed):
  def fn_generator(val):
    while True: 
      val = fn(val[1])
      if val == False: break
      yield val[0]
  return [i for i in fn_generator([None, seed])]
f = lambda n: False if n > 40 else [-n, n + 10]
print(unfold(f, 10))

Sample Output:

[-10, -20, -30, -40]


Flowchart: Builds a list, using an iterator function and an initial seed value.

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Next: Write a Python program to map the values of a list to a dictionary using a function, where the key-value pairs consist of the original value as the key and the result of the function as the value.

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Python: Tips of the Day

Decapitalizes the first letter of a string:


def tips_decapitalize(s, upper_rest=False):
  return s[:1].lower() + (s[1:].upper() if upper_rest else s[1:])
print(tips_decapitalize('PythonTips', True)) 




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