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.

…

Continue reading “How Do You Troubleshoot the Python Errors “NameError: name ‘copy’ is not defined” or “object has no attribute ‘copy’”?”

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; …

Continue reading “How Do You Write a Python Function to Determine if There Are Three or More Unique Characters in a String?”

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.

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

Problem scenario
You are running a Python script. You keep getting “SyntaxError: invalid syntax” and a line number. You can find nothing wrong with the syntax on the specified line number. What do you do?

Possible solution #1
Look at the line with code, as opposed to blank line(s), above it. Is there a missing quote, brace, bracket or parentheses?

Possible solution #2
Are you trying to use an “if” statement on one line?

…

Continue reading “How Do You Troubleshoot “SyntaxError: invalid syntax” in Python?”

Problem scenario
You have a list in Python that you copy into another variable. You change the original list and the copied version changes. Why does the copied version get copied and what can you do to overcome this?

Solution
There is something called a “deep” copy and a “shallow” copy. This program will illustrate both the problem and the solution:

list_a = [3, …

Continue reading “Why in Python Does a Variable Copy Get Changed when You Change Its Source?”

Problem scenario
You want to use the copy feature in Python. What do you do?

Solution
To see the different types of copying, use a mutable object such as a list. Here is an example:

import copy

var1 = [1, 2, 3, 4]
shallow_copy = var1
deep_copy = copy.deepcopy(var1)
var1.append(999999999999)

print()
print(shallow_copy)
print(” — Shallow copy above and deep copy below —.”)
print(deep_copy)

For most (or perhaps all) intents and purposes,

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Continue reading “How Do You Use the .copy() Feature in Python?”