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]
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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.
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Python: Tips of the Day
Find current directory and file's directory:
To get the full path to the directory a Python file is contained in, write this in that file:
import os dir_path = os.path.dirname(os.path.realpath(__file__))
(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)
To get the current working directory use
import os cwd = os.getcwd()
Documentation references for the modules, constants and functions used above:
- The os and os.path modules.
- The __file__ constant
- os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
- os.path.dirname(path) (returns "the directory name of pathname path")
- os.getcwd() (returns "a string representing the current working directory")
- os.chdir(path) ("change the current working directory to path")
Ref: https://bit.ly/3fy0R6m
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