Strings and Substrings

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Questions and Answers

Given the nuances of Python's dynamic typing, which of the following scenarios would result in a TypeError only during runtime, assuming no prior explicit type conversions, and given that the interpreter encounters these lines sequentially?

  • `flag = "True"; print(not flag)`
  • `name = "Alice"; print(name.upper() + 10)` (correct)
  • `pi = "3.14"; result = pi * 2`
  • `age = "25"; print(age + 5)`

Consider a scenario where you are parsing a complex data file, and you encounter the following Python code block. What would be the state of the error_log variable after executing this code block, assuming the file stream data_file contains inconsistent line endings (i.e., a mix of \r\n and \n) and non-UTF-8 encoded characters?

  • A string consisting of `UnicodeDecodeError` followed by `Line processing completed.` concatenated.
  • A string containing the *first* successfully decoded line, followed by `Line processing completed.`.
  • A string consisting of only `Line processing completed.`
  • A multiline string containing all processed lines, interspersed with `UnicodeDecodeError` messages and incomplete lines due to encoding issues. (correct)

In the context of advanced data manipulation, which of the following approaches would be most efficient for extracting all numerical substrings (including integers and floating-point numbers) from a very large string (e.g., 1GB) containing mixed alphanumeric characters and symbols, while minimizing memory footprint and execution time?

  • Utilizing `str.split()` to split the string by non-numeric characters followed by filtering and converting valid numeric strings in a list comprehension.
  • Using Python's `re.findall(r'\d+\.?\d*', large_string)` after loading the entire string into memory.
  • Leveraging a combination of `mmap.mmap` to memory-map the large string and a compiled regular expression (`re.compile`) with `re.finditer` to iteratively find and convert numerical substrings. (correct)
  • Employing a generator expression with `re.finditer(r'\d+\.?\d*', line)` to process the string line by line, assuming the string can be split into reasonable line sizes, and converting each match to a float.

Given a scenario where you are tasked with implementing a custom string interning mechanism in Python (similar to how Python interns small integers and strings), which of the following approaches would provide the most memory-efficient and thread-safe solution for managing a large number of dynamically created strings?

<p>Creating a custom C extension module that directly manipulates Python's internal string representation (<code>PyStringObject</code>) using the Python C API, and ensuring thread safety through the Global Interpreter Lock (GIL). (C)</p> Signup and view all the answers

Consider the following code snippet aiming to reverse a string in-place (without using extra memory). Under what conditions would the function fail to correctly reverse specific Unicode strings and what is the root cause?

<p>It fails when the string contains surrogate pairs because the swap operation splits the pairs, leading to invalid Unicode characters. (C)</p> Signup and view all the answers

Assuming you are working on a legacy system with limited memory and processing power, which string concatenation method would be the most resource-efficient (in terms of both CPU cycles and memory allocation) when building a very long string from a series of smaller strings?

<p>Utilizing a <code>io.StringIO</code> object to accumulate string fragments and then retrieving the final string. (C)</p> Signup and view all the answers

Given a complex scenario where you need to parse a string containing nested, escaped delimiters (e.g., "{value1: \"inner_value\", value2: data}"), which of the following approaches would be most robust and least prone to errors?

<p>Leveraging a dedicated parsing library like <code>pyparsing</code> or <code>lark</code> with a grammar defined to handle the nested structure and escaping. (A)</p> Signup and view all the answers

You're building a high-performance application that requires frequent string comparisons. Which of the following practices would result in the most significant performance improvement?

<p>Interning frequently compared strings using <code>sys.intern()</code> to ensure that equal strings share the same memory address. (B)</p> Signup and view all the answers

In the context of secure coding practices, which of the following methods offers the most robust protection against format string vulnerabilities when constructing dynamic strings in Python, especially when dealing with user-supplied input?

<p>Using <code>string.Template</code> with safe substitutions to prevent arbitrary code execution. (C)</p> Signup and view all the answers

Given a scenario where you have a very large number of strings (millions) and you need to efficiently determine the frequency of all substrings of length k within those strings, which approach minimizes memory usage and maximizes processing speed, assuming all strings are encoded in UTF-8?

<p>Leveraging a suffix tree data structure implemented in a compiled language (e.g., C++) to index all strings and efficiently query the frequency of substrings of length <code>k</code>. (B)</p> Signup and view all the answers

Flashcards

What is a string?

A piece of information enclosed in quotation marks.

What is a substring?

A portion of a larger string.

Strings holding numbers

Strings can contain numerals, but they are still treated as text, not numbers.

Multiline String

A string that spans multiple lines in the code, created using triple quotes.

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Study Notes

Strings

  • A string is a piece of information enclosed in quotation marks.
  • Strings are also referred to as string literals.
  • Strings can be declared using either single or double quotes - both work the same.
  • Strings can be many words long.
  • Strings can contain numbers.

Substrings

  • A substring is a part of an existing string.

Strings and Numbers

  • Strings can consist of just numbers, but they are still considered strings.
  • Doing mathematical operations with number strings will cause errors, thus data type conversion is important.

Multiline Strings

  • Multiline strings can hold large amounts of text spanning multiple lines of code.
  • Multiline strings are created using three sets of quotes (either double or single) before and after the text.

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