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:

Visualize Python code execution:
The following tool visualize what the computer is doing step-by-step as it executes the said program:
Python Code Editor:
Have another way to solve this solution? Contribute your code (and comments) through Disqus.
Previous: Write a Python program to sort one list based on another list containing the desired indexes.
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.
What is the difficulty level of this exercise?
Test your Programming skills with w3resource's quiz.
Python: Tips of the Day
Decapitalizes the first letter of a string:
Example:
def tips_decapitalize(s, upper_rest=False): return s[:1].lower() + (s[1:].upper() if upper_rest else s[1:]) print(tips_decapitalize('PythonTips')) print(tips_decapitalize('PythonTips', True))
Output:
pythonTips pYTHONTIPS
- Weekly Trends
- Java Basic Programming Exercises
- SQL Subqueries
- Adventureworks Database Exercises
- C# Sharp Basic Exercises
- SQL COUNT() with distinct
- JavaScript String Exercises
- JavaScript HTML Form Validation
- Java Collection Exercises
- SQL COUNT() function
- SQL Inner Join
- JavaScript functions Exercises
- Python Tutorial
- Python Array Exercises
- SQL Cross Join
- C# Sharp Array Exercises
We are closing our Disqus commenting system for some maintenanace issues. You may write to us at reach[at]yahoo[dot]com or visit us at Facebook