Problem Scenario
Rotating a list can make it appear circular (wherein an iteration from the last element brings you to the first element in the list). You do not want to import any modules. You have a list called foobar. You want to keep the content the same, but adjust the index by 1 on each value. How do you rotate a list in Python?

Solution

foobar = foobar[-1:] + foobar[:-1] …

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Problem scenario
You want to write a palindromic testing program without importing any modules that ignores a string’s punctuation or spaces. What do you do?

Solution
Use this program:

def is_palindrome(s: str) -> bool:
# i moves forward, and j moves backward
i, j = 0, len(s) -1
while i < j:
while not s[i].isalnum() and i < j:
i += 1
while not s[j].isalnum() and i < …

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Problem scenario
You are running a Python program. But you get “NameError: name ‘copy’ is not defined” or “object has no attribute ‘copy'”. What should you do?

Solution
Use “import copy” at the top of the program.

…

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Problem scenario
You want a function to tell you if there are three unique characters in a string. For example “ababababa” would have fewer than three unique characters. But “abc” would have three or more unique characters. How do you write a function that does this that solves in linear time?

Solution

variable_to_test = “aaaaaaaaaaaabbbbbb”

def two_unique(s):
flag = “There are only two unique characters in the string!”
dict_a = {}
for string_portion in s:
if string_portion in dict_a:
pass
else:
dict_a[string_portion] = 1
key_counter = 0
for key in dict_a.keys():
key_counter = key_counter + 1; …

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Problem scenario
List operations such as .sort() will change previous copies of the list.

String operations such as .replace(“old_pattern”, “new_pattern”, count), will not change the variable or its copies; these operations will return a string after the replace operation has run on the original string.

Why is this behavior happening?

Solution
In-place changes and mutability are factors.

…

Continue reading “Why Are Python List Operations/Methods Unlike Python String Operations/Methods?”