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Questions and Answers

Given the code import tkinter.messagebox and messagebox.showinfo("Hello"), which two statements are correct regarding the function and its environment?

  • `messagebox` is a module or a package. (correct)
  • The `messagebox()` function can also be invoked using `messagebox()`.
  • The `messagebox()` function can be invoked using `tkinter.messagebox()`.
  • The `showinfo()` function is contained in `the messagebox` module. (correct)

Which two statements about Python packages and modules are incorrect?

  • A programmer is obliged to manually create a directory/folder named `__pycache__` inside every package. (correct)
  • The extension `.pby ` marks files containing Python semi-compiled byte-code. (correct)
  • A variable named `__name__` is a string containing the module name.
  • A source file named `__init__.py` is used to mark a directory/folder as containing a Python package and to initialize the package's state.

Which two statements about Python module search paths and variable privacy are correct?

  • The directory from which the Python code is run is always searched through in order to find the necessary modules. (correct)
  • The directory from which the code is run is never searched through.
  • Variables with names starting with two underscores are considered private inside their home module. (correct)
  • Variables with names ending with two underscores are considered private inside their home module.

What is the output of the following Python code?

import math
x = 1.7
print(-abs(math.floor(x) + math.ceil(x)))

<p>-3 (A)</p> Signup and view all the answers

Which function is used to list all the names defined in a module?

<p><code>dir()</code> (B)</p> Signup and view all the answers

To determine if a hardware platform uses an x86 or ARM CPU, which two functions can be used?

<p><code>platform()</code> (B), <code>processor()</code> (D)</p> Signup and view all the answers

Which two operations in Python will not raise an exception under normal circumstances?

<p>Slicing a string. (A), Decrementing an integer variable by one. (C)</p> Signup and view all the answers

What is the expected output of the code snippet?

<p>out of order (A), turn on (D)</p> Signup and view all the answers

What is the expected output of the following code?

<p>('list index out of range',) (D)</p> Signup and view all the answers

Which of the following statements are true?

<p>Python accepts UTF-8 encoded source files. (C), ASCII is a subset of UNICODE. (D)</p> Signup and view all the answers

Which of the following snippets output 123 to the screen?

<pre><code class="language-tmp">tmp.sort() print(''.join(tmp))``` (C), `print(''.join(sorted(&quot;321&quot;)))` (D) </code></pre> Signup and view all the answers

Which of the following expressions evaluates to True and raises no exception?

<p><code>10 != '1' + '0'</code> (A)</p> Signup and view all the answers

Given the following Python code, which two expressions evaluate to True?

<p><code>selection.my_ID == 2</code> (B), <code>isinstance(start, Button)</code> (C)</p> Signup and view all the answers

What is the output of the code snippet below?

<p>8 (A)</p> Signup and view all the answers

Which two of the following lines contain valid Python code?

<p><code>lambda a,b: a if a &lt; b else b</code> (B), <code>lambda a,b: True</code> (C)</p> Signup and view all the answers

The errno.ENOENT symbol corresponds to which error?

<p>No such file or directory (C)</p> Signup and view all the answers

Which function reads one line from a text file?

<p><code>readline()</code> (C)</p> Signup and view all the answers

What is the expected output of the code snippet below?

<p>2 (B)</p> Signup and view all the answers

What is the output of the code?

<p>-1 (A)</p> Signup and view all the answers

Given the following code, which two expressions evaluate to True without raising an exception?

<p><code>isinstance(d, Un)</code> (B), <code>Troi in Quatre.__bases__</code> (C)</p> Signup and view all the answers

What is the expected output of the following code snippet?

<p>It outputs <code>261</code> (B)</p> Signup and view all the answers

Which two statements are true about object-oriented programming?

<p>A class may exist without its objects, but an object cannot exist without its class. (A), Encapsulation is a phenomenon which allows you to hide some class traits from the outer world. (B)</p> Signup and view all the answers

Given the class hierarchy, which two class declarations are permissible and will not raise an exception?

<p><code>class Jewel(Adamant, Gem): pass</code> (A), <code>class Jewel(Diamond, Adamant): pass</code> (D)</p> Signup and view all the answers

Which of the following Python classes contains a usable constructor?

<p>All of the above (D)</p> Signup and view all the answers

What would be the result of the following code?

<p>An AttributeError (B)</p> Signup and view all the answers

Assuming that the following code has been successfully executed, indicate which statement is correct?

<p><code>Volume.dict ['chapter'] != None</code> (D)</p> Signup and view all the answers

Which of the following Python string operations will result in an error, assuming s has been assigned a value? (Select two answers.)

<p><code>S = s[9]</code> given <code>S = 'rhyme'</code> (A), <code>S = s[-3:-5]</code> given <code>S = &quot;12&quot;</code> (C)</p> Signup and view all the answers

Which of the following are not valid Python string literals? (Select two answers.)

<p><code>'Whether ''tis nobler in the mind to suffer'</code> (A), <code>'''To be, or not to be, that is the question&quot;&quot;&quot;</code> (D)</p> Signup and view all the answers

Which of the following expressions evaluate to True and raise no exception? (Select two answers.)

<p><code>'de' not in 'abc'</code> (C), <code>not 'xyz' in 'uvwxyz'</code> (D)</p> Signup and view all the answers

Given the class below, which method will correctly provide the value of the rack variable?

<pre><code class="language-def"> return self.rack``` (D) </code></pre> Signup and view all the answers

Given the code below, which code lines correctly decrement the b variable by one? (Select two answers.)

<p><code>A.b -=1</code> (B), <code>object.b -= 1</code> (D)</p> Signup and view all the answers

Flashcards

messagebox in tkinter

A module or package holding the showinfo() function.

Purpose of .pyc files and __init__.py

Files containing Python semi-compiled byte-code. Also,__init__.py marks a directory as a Python package.

Module search path include current directory?

The directory from which Python code is run is searched for modules.

Output of print(-abs(math.floor(x) + math.ceil(x))) when x = 1.7

The code will output -3. math.floor(1.7) is 1, math.ceil(1.7) is 2, therefore -(1 + 2) is -3.

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List module contents

The dir() function lists a module's contents.

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Determine hardware platform (x86 or ARM)

processor() and platform() functions reveal CPU architecture.

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Operations that don't raise exception

Decrementing an integer and slicing a string never raise exceptions assuming valid syntax.

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What does isinstance() do?

Checks if an object is an instance of a class or its subclasses.

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What is Method Resolution Order (MRO)?

The order in which base classes are searched when looking for a method or attribute in a class hierarchy. Python uses Depth-First Left-to-Right

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What is Polymorphism?

The most specific version of a method that is appropriate for the type of object in hand is used. Determined at runtime.

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What is Encapsulation?

Bundling the data (attributes) and methods (functions) that operate on that data into a single unit (class), and restricting access to some of the class's components.

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What is a Class?

A blueprint for creating objects (instances). It defines the attributes and methods that the objects will have.

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What is an Object?

A specific instance of a class. Each object has its own unique data, but shares the methods defined by the class.

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What does __init__ do?

A special method used to initialize the attributes of an object when it is created from a class (__init__).

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What is a Subclass?

A class that inherits attributes and methods from another class (the superclass or parent class).

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Exception Handling Output

Prints 'turn on' then 'out of order' because the exception is caught and its string representation is printed.

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List Index Error Output

Prints ('list index out of range',) because accessing data[-3] attempts to access an index outside the bounds of the list, triggering an exception which prints the exception message.

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Assertion Error Handling

Prints an error message because the assertion in attic(x) fails when x is 0, leading to an AssertionError which is not handled, thus crashing the program.

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ValueError Handling

Prints 2. The try block attempts to convert the string 'three' to an integer, which raises a ValueError and is caught by the except block, assigning 2 to e.

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String Encoding (True Statements)

\n encodes a new-line character and ASCII is a subset of UNICODE.

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Sorting Strings

''.join(sorted("321")) and the block of code with list conversion, sorting and joining produce 123.

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String Manipulation and Indexing

  1. The code removes commas from the string, resulting in 'John Doe 42', then it prints the character at index -2, which is '4'.
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Looping and Membership Testing

  1. The code iterates through '+-+-+'. Because the if statement checks if the character is NOT IN the header, nothing happens so it prints 0.
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What is isinstance()?

Checks if an object is an instance of a class or a subclass thereof.

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What is a higher-order function?

A function that takes another function as an argument or returns a function.

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What is a lambda function?

An anonymous, small, single-expression function.

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S[-1]

Accesses the last character of the string 'S'. Negative indices count from the end.

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Invalid String Literals

String literals that are not valid include unterminated strings or those with mismatched quotes.

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What is errno.ENOENT?

The error code for 'No such file or directory'.

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in and not in with strings

not in returns True if the substring is not found. 'T' in 'de' returns False because 'T' is in 'de'.

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What does readline() do?

To read a single line from a text file.

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What does input() do?

Reads data from the standard input stream (keyboard).

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Class vs. Instance Variables

The code outputs False because Content.title is initialized only once and shared across all instances. text1.title remains "None", while text2.name becomes "Article than None".

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hasattr() function

hasattr(object, 'attribute') checks if an object has a given attribute.

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What are the three pre-opened file streams?

Standard input, standard output, and standard error.

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What does readlines() do?

Returns a list of strings, each representing a line from the file.

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__str__ Method Error

When a __str__ method tries to use a variable name that is not defined, it produces an error.

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Correct get Method definition

The method needs to be properly defined and have a "self" parameter to access the class's variables.

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Decrementing Class Variables

A.b -= 1 correctly decrements the class variable b. Instance variables are accessed using object.b.

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Study Notes

  • The showinfo() function is in the messagebox module.
  • The messagebox is a module or package.
  • The .pyc extension marks files containing Python semi-compiled byte-code.
  • A source file named init.py marks a directory/folder as containing a Python package and initializes the package's state.
  • Variables starting with two underscores are considered private inside their home module.
  • The directory from which the Python code is run is always searched through to find the necessary modules.
  • The code import math; X = 1.7; print(-abs (math.floor(x) + math.ceil(x))) will output the value -3
  • The dir() function is used to reveal a module's contents.
  • The processor() and platform() functions can determine if a hardware platform utilizes the x86 or arm CPU.
  • Decrementing an integer variable and slicing a string will not raise an exception.
  • The following messages appear when the code is run:
  • turn on
  • out of order
  • The expected output of the code provided is ('list index out of range',)
  • The expected output of the code provided is 2
  • The code will output the value 2
  • ASCII is a subset of UNICODE
  • Python accepts UTF-8 encoded source files.
  • The code print(''.join(sorted("321"))) and tmp = list("321"); tmp.sort(); print(''.join(tmp)) will both output "123"
  • The code provided will print out the character 4
  • The expected output of the following code is the integer 0
  • The expression 10 != '1' + '0' evaluates to True and will not exceptions.
  • String assignments that produce a non-empty string:
  • S = "12"; S = s[1::2]
  • S = "12"; S = s[-1]
  • The code returns the value False.

Valid & Invalid String Literals

  • The following are invalid or not valid string literals
  • "\\"
  • "this is a quote: \""
  • The following expressions evaluate to True and do not raise an exception:
  • T in "T"
  • 'de' not in 'abc'
  • The provided code will output False.
  • The code will output True False.
  • The proper solution to get the class variable is definition Def get (self): return self.rack
  • The code lines that correctly decrement the b variable by one:
  • object.A.b -= 1
  • A.b -= 1
  • The following expressions evaluate to True:
  • isinstance(d, Un)
  • Troi in Quatre.__bases__
  • The expressions that evaluate to True are as follows:
  • Volume.__dict__['chapter'] != None
  • 'paragraph' in edition.__dict__
  • The code will output 261
  • The statements that are true about object oriented programming:
  • A class may exist without its objects, but an object cannot exist without its class.
  • Encapsulation is a phenomenon that allows you to hide some class traits from the outer world.
  • Permissible class declarations that won't raise an exception:
  • class Jewel (Adamant, Gem): pass
  • class Jewel (Adamant, Diamond): pass
  • The following classes contain a usable constructor:
  • class Lower: def __init__(self): self.color = "blue"
  • class Working: def init (self): raise KeyError
  • isinstance (start, Button)
  • selection.my_ID != 2
  • The code will output the number 8 based on the cube(2) call.
  • The following lines contain valid Python code:
  • lambda a,b: a if a < b else b
  • lambda a,b: True
  • The errno.ENOENT symbol refers to an error described as No such file or directory.
  • The function to use to read one line from a text file is readline()
  • The provided code will output the integer 4
  • The expected output of the code provided is 2
  • The provided code will result in an error message on the screen.
  • The statements that are true include:
  • The input() function reads data from the stdin stream.
  • There are three pre-opened file streams.
  • The code will output True.

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