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notebook 04: move part of exercise 4.2 to Additional Exercises
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,75 +1,40 @@ | ||
| # Exercise 4.3 | ||
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| # 1. What does is_part_of_set do? | ||
| # ******************************* | ||
| from exercise_43_module import is_part_of_set | ||
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| # help(is_part_of_set) | ||
| # "is_part_of_set()" returns True if its argument is a prime number | ||
| # and False otherwise. | ||
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| for n in range(10): | ||
| print(n, "->", is_part_of_set(n)) | ||
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| # 2 and 3. Use is_part_of_set to get all primes numbers between 2 and 50000 | ||
| # ************************************************************************* | ||
| from exercise_43_module import is_part_of_set | ||
| from time import time | ||
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| primes = [] | ||
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| # Get the current time, so we can compute elapsed time at the end. | ||
| t0 = time() | ||
| for i in range(50000): | ||
| if is_part_of_set(i): | ||
| primes.append(i) | ||
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| time_first_algo = time() - t0 | ||
| print("it took", time_first_algo, "seconds") | ||
| print("found", len(primes), "prime numbers") | ||
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| # Optional: devise a more time efficient way of getting the prime numbers | ||
| # *********************************************************************** | ||
| # | ||
| # Principle: rather than testing each number separately, we test the whole | ||
| # set of numbers at once by going over all number and "eliminating" all | ||
| # multiples of that number. | ||
| from time import time | ||
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| t0 = time() | ||
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| # Phase1 : initialization | ||
| upperLimit = 50000 | ||
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| # Create a list that contains True for all numbers we want to test. | ||
| # During the algorithm we will set all non-prime numbers to False. | ||
| arePrime = [True] * (upperLimit + 1) | ||
| arePrime[0] = False # 0 is not prime | ||
| arePrime[1] = False # 1 is not prime | ||
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| # Phase2 : go through all numbers | ||
| primes2 = [] | ||
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| for i in range(2, upperLimit + 1): # for each candidate number | ||
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| # only do something if that number has not been set as a non-prime before | ||
| if arePrime[i]: | ||
| primes2.append(i) | ||
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| # then we want to set all multiples of that number as non-prime | ||
| mult = 2 * i | ||
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| # all multiples until the upper limit is reached | ||
| while mult <= upperLimit: | ||
| arePrime[mult] = False # set the multiple to non-prime | ||
| mult += i # nest multiple | ||
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| time_second_algo = time() - t0 | ||
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| print("it took", time() - t0, "seconds") | ||
| print("speedup compared to first algorithm:", time_first_algo / time_second_algo) | ||
| print("found", len(primes2), "prime numbers") | ||
| print("is this list the same as with the first algorithm ?", primes == primes2) | ||
| import os # Import the os module into the global namespace. | ||
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| # We re-use the function from exercise 4.2, and add an optional argument | ||
| # "ignore_hidden" that, when set to "True", will ignore hidden files (i.e. | ||
| # files whose name is starting with a dot, e.g. ".DS_Store") | ||
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| def count_files(dir_name, ignore_hidden=False): | ||
| """Counts files present in the input directory. | ||
| Only files are counted, directories are ignored. | ||
| Arguments: | ||
| dir_name: path of directory in which to count files. | ||
| ignore_hidden: Optional. If set to True, hidden files (files that | ||
| start with a '.') are ignored from the count. | ||
| """ | ||
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| # Initialize file counter. | ||
| file_count = 0 | ||
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| # Loop through all files and directories present in the input directory. | ||
| for f in os.listdir(path=dir_name): | ||
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| # Get the absolute path of the file/directory. | ||
| full_path = os.path.join(dir_name, f) | ||
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| # Verify the path corresponds to a file, not a directory. | ||
| if os.path.isfile(full_path) and not (ignore_hidden and f.startswith(".")): | ||
| file_count += 1 | ||
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| return file_count | ||
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| parent_dir = os.path.dirname(os.getcwd()) | ||
| print("File count in [", parent_dir, "]: ", count_files(parent_dir), sep="") | ||
| print( | ||
| "File count (excluding hidden files) in [", parent_dir, "]: ", | ||
| count_files(parent_dir, ignore_hidden=True), | ||
| sep="" | ||
| ) |
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