MAT 215 Chapter 8

Which of the following statements a), b) or c) is false? a. By default, the re module's sub function replaces only the first occurrence of a pattern with the replacement text you specify. The statement re.sub(r'\t', ', ', '1\t2\t3\t4') returns '1, 2\t3\t4' b. The sub function receives three required arguments—the pattern to match, the replacement text and the string to be searched and returns a new string. c. The sub function's keyword argument count can be used to specify the maximum number of replacements. d. All of the above statements are true. '

Answer: a. Actually, by default, the re module's sub function replaces all occurrences of a pattern with the replacement text you specify, so the statement returns '1, 2, 3, 4

Which of the following statements a), b) or c) is false? a. Python has separate string and character types. b. You can use string method isdigit when validating user input that must contain only digits. c. String method isalnum returns True if the string on which you call the method is alphanumeric—that is, it contains only digits and letters. d. All of the above statements are true.

Answer: a. Actually, in Python, a character is simply a one-character string

Which of the following statements a), b) or c) is false? a. Strings support many of the same sequence operations as sets, lists and tuples. b. Strings, like tuples, are immutable. c. The re module can be used to match patterns in text. d. All of the above statements are true. .

Answer: a. Actually, strings support many of the same sequence operations as lists and tuples— sets are not sequences

Which of the following statements is false? a. The d presentation type in the following f-string formats strings as integer values: f'{10:d}' b. The integer presentation types b, o and x or X format integers using the binary, octal or hexadecimal number systems, respectively. c. The c presentation type in the following f-string formats an integer character code as the corresponding character: f'{65:c} {97:c}' d. If you do not specify a presentation type, as in the second placeholder below, non-string values like the integer 7 are converted to strings: f'{"hello":s} {7}'

Answer: a. Actually, the d presentation type formats integer values as strings.

Which of the following statements a), b) or c) is false? a. Method replace takes two substrings. It searches a string for the substring in its first argument and replaces each occurrence with the substring in its second argument. The method returns a new string containing the results. b. The following code replaces tab characters with commas: values = '1\t2\t3\t4\t5' values.replace('\t', ', ') c. Method replace can receive an optional third argument specifying the maximum number of replacements to perform. d. All of the above statements are true.

Answer: b. Actually, this code replaces each tab character with a comma followed by a space. The following code replaces each tab character with just a comma: values = '1\t2\t3\t4\t5' values.replace('\t', ',')

Consider this text from Shakespeare's Romeo and Juliet: soliloquy = 'To be or not to be, that is the question' Which of the following statements a), b) or c) is false? a. String method index searches for a substring within a string and returns the first index at which the substring is found; otherwise, a ValueError occurs. The following code returns 3: soliloquy.index('be') b. String method rindex performs the same operation as index, but searches from the end of the string and returns the last index at which the substring is found; otherwise, a Value-Error occurs. The following code returns 3: soliloquy.rindex('be') c. String methods find and rfind perform the same tasks as index and rindex but, if the substring is not found, return -1 rather than causing a Value-Error. d. All of the above statements are true.

Answer: b. Actually, this code returns 16.

Preparing data for analysis is called ________. a. data wrangling b. data munging c. Both (a) and (b). d. Neither (a) nor (b).

Answer: c

Which of the following statements is false? a. The following f-string formats the float value 17.489 rounded to the hundredths position: f'{17.489:.2f}' b. Python supports precision only for floating-point and Decimal values. c. Formatting is type dependent—if you try to use .2f to format a string like 'hello', a NameError occurs. d. The presentation type f in the format specifier .2f is required.

Answer: c. Actually, a ValueError occurs.

Which of the following statements is false? a. The regular-expression metacharacter \ begins each of the predefined regular-expression character classes, which each match a specific set of characters. b. The following code ensures that a string contains five consecutive digits: re.fullmatch(r'\d{5}', '02215') c. A character class is a regular expression escape sequence that matches one or more characters. d. The following code returns None because '9876' contains only four consecutive digit characters. re.fullmatch(r'\d{5}', '9876')

Answer: c. Actually, a character class is a regular expression escape sequence that matches exactly one character

Which of the following statements is false? a. The re module's findall function finds every matching substring in a string and returns a list of the matching substrings. b. The following code extracts all phone numbers of the form ###-###-#### from a string: contact = 'Wally White, Home: 555-555-1234, Work: 555-555-4321' re.findall(r'\d{3}-\d{3}-\d{4}', contact) c. The re module's finditer function works like findall, but returns a greedy iterable of match objects. d. For large numbers of matches, using finditer can save memory because it returns one match at a time, whereas findall returns all the matches at once.

Answer: c. Actually, function finditer works like findall, but returns a lazy iterable of match objects

Which of the following statements a), b) or c) is false? a. String method splitlines returns a list of strings representing the lines of text split at each newline character in the original string. b. Python stores multi-line strings with embedded \n characters to represent the line breaks. c. For the string lines = """This is line 1 This is line2 This is line3""" the statement lines.splitlines(True) keeps the newlines and returns: ['This is line 1', '\nThis is line2', '\nThis is line3'] d. All of the above statements are true.

Answer: c. Actually, in this case, splitlines keeps the newlines at the end of each line and returns: ['This is line 1\n', 'This is line2\n', 'This is line3']

Which of the following statements a), b) or c) is false? a. A space before the presentation type in an f-string indicates that positive numbers should show a space character in the sign position. This is useful for aligning positive and negative values for display purposes, as in: In [1]: print(f'{27: d}\n{-27: d}') 27 -27 b. If a field width is specified with a space flag, the space should appear before the field width. c. You can format numbers with thousands separators by using a comma (,), as in the following f-strings: f'{,12345678:d}' f'{,123456.78:.2f}' d. All of the above statements are true.

Answer: c. Actually, the comma (,) must appear in the format specifier to the right of the colon, as in the following f-strings: f'{12345678:,d}' f'{123456.78:,.2f}'

Which of the following statements is false? a. f-strings were added to Python in Python 3.6. b. You'll often see the format method in the Python documentation and in the many Python books and articles written before f-strings were introduced. c. The following code formats the float value 17.489 rounded to the hundredths position: '{:.3f}'.format(17.489) d. All of the above statements are true.

Answer: c. Actually, the following code formats the float value 17.489 rounded to the hundredths position: '{:.2f}'.format(17.489)

Which of the following statements is false? a. String method split with no arguments tokenizes a string by breaking it into substrings at each whitespace character, then returns a list of tokens. b. To tokenize a string at a custom delimiter (such as each comma-and-space pair), specify the delimiter string (such as, ', ') that split uses to tokenize the string, as in: letters = 'A, B, C, D' letters.split(', ') c. If you provide an integer as split's second argument, it specifies the maximum number of splits. The last token is the remainder of the string after the maximum number of splits. Assuming the string in Part (b), the code letters.split(', ', 1) returns ['A', 'B', 'C, D'] d. There is also an rsplit method that performs the same task as split but processes the maximum number of splits from the end of the string toward the beginning.

Answer: c. Actually, the output shown would require the second argument 2. The output of the code in Part (c) is ['A', 'B, C, D']

Which of the following statements a), b) or c) is false? a. Strings can be compared with the comparison operators. Recall that strings are compared based on their underlying integer numeric values. So uppercase letters compare as less than lowercase letters because uppercase letters have lower integer values. b. You can check character codes with ord. For example, the following code displays the values 65 and 97 for A and a, respectively: print(f'A: {ord("A")}; a: {ord("a")}') c. In the following interactive session that compares the strings 'Orange' and 'orange', the outputs of snippets [2] and [6] (marked as ???) are False and True: In [1]: 'Orange' == 'orange' Out[1]: False In [2]: 'Orange' != 'orange' Out[2]: ??? In [3]: 'Orange' < 'orange' Out[3]: True In [4]: 'Orange' <= 'orange' Out[4]: True In [5]: 'Orange' > 'orange' Out[5]: False In [6]: 'Orange' >= 'orange' Out[6]: ??? d. All of the above statements are true.

Answer: c. Actually, the outputs of snippets [2] and [6] are True and False

Assuming the following two-dimensional list: contacts = [['Mike Green', '[email protected]', '5555555555'], ['Sue Brown', '[email protected]', '5555551234']] Which of the following statements a), b) or c) is false? a. The following code creates a DataFrame from the list: contactsdf = pd.DataFrame(contacts, columns=['Name', 'Email', 'Phone']) b. Part (a) specified column indices via the columns keyword argument but did not specify row indices, so the rows are indexed from 0. c. The following output shows how the DataFrame is displayed when you evaluate the variable contactsdf in IPython—all column values are right aligned by default, as they are in Python: Name Email Phone 0 Mike Green [email protected] 5555555555 1 Sue Brown [email protected] 5555551234 d. All of the above statements are true.

Answer: c. Actually, this differs from Python formatting in which numbers in a field are right aligned by default but non-numeric values are left aligned by default.

Consider the following code that demonstrates regular expressions containing literal characters—that is, characters that match themselves: In [1]: import re In [2]: pattern = '02215' In [3]: 'Match' if re.fullmatch(pattern, '02215') else 'No match' Out[3]: 'Match' In [4]: 'Match' if re.fullmatch(pattern, '51220') else 'No match' Out[4]: 'No match' Which of the following statements a), b) or c) is false? a. The re module's fullmatch function's first argument is the regular expression pattern to match. Any string can be a regular expression. The variable pattern's value, '02215', contains only literal digits that match themselves in the specified order. b. The second argument to fullmatch is the string that should entirely match the pattern. If the second argument matches the pattern in the first argument, fullmatch returns an object containing the matching text, which evaluates to True. c. In snippet [4], the second argument contains the same digits as the regular expression, but in a different order. This is still a match and fullmatch returns an object containing the matching text, which evaluates to True. d. All of the above statements are true.

Answer: c. Actually, this is not a match, because the digits are not in the correct order, so fullmatch returns None, which evaluates to False

Which of the following statements is false? a. Before working with text data, you'll often use regular expressions to validate the data. b. A U.S. Social Security number contains three digits, a hyphen, two digits, a hyphen and four digits, and adheres to other rules about the specific numbers that can be used in each group of digits. c. You must create your own regular expressions to ensure that they'll meet your needs. d. Many sites provide interfaces in which you can test regular expressions.

Answer: c. Actually, you'll rarely need to create your own regular expressions for common items. Repository websites like https://regex101.com, http://www.regexlib.com, https://www.regular-expressions.info and others offer existing regular expressions that you can copy and us

Which of the following statements a), b) or c) is false? a. String method count returns the number of times its argument occurs in the string on which the method is called. b. If you specify as the second argument to method count a start_index, as in sentence.count('to', 12) count searches only the slice string[start_index:]—that is, from start_index through end of the string. c. If you specify as the second and third arguments of method count the start_index and end_index, as in sentence.count('that', 12, 25) count searches only the slice string[start_index:end_index]—that is, from start_index up to, but notincluding, end_index. d. All of the above statements are true.

Answer: d

Which of the following statements a), b) or c) is false? a. String methods lower and upper can convert strings to all lowercase or all uppercase letters, respectively. b. Method capitalize copies the original string and returns a new string with only the first letter capitalized (sometimes called sentence capitalization). . Method title copies the original string and returns a new string with only the first character of each word capitalized (sometimes called book-title capitalization). d. All of the above statements are true.

Answer: d

Which of the following statements a), b) or c) is false? a. The re module's search function looks in a string for the first occurrence of a substring that matches a regular expression and returns a match object (of type SRE_Match) that contains the matching substring. The match object's group method returns that substring, as in the following session: In [1]: import re In [2]: result = re.search('Python', 'Python is fun') In [3]: result.group() if result else 'not found' Out[3]: 'Python' b. Function search returns None if the string does not contain the pattern. c. You can search for a match only at the beginning of a string with function match. d. All of the above statements are true.

Answer: d

Which of the following statements a), b) or c) is false? a. You can force the sign on a positive number to display, as in: f'[{27:+10d}]' b. The + before the field width in Part (a) specifies that a positive number should be preceded by a +. A negative number always starts with a -. c. To fill the remaining characters of a field with 0s rather than spaces, place a 0 before the field width (and after the + if there is one), as in: f'[{27:+010d}]' d. All of the above statements are true. .

Answer: d

Which of the following statements a), b) or c) is false? In addition to validating data, regular expressions often are used to: a. Extract data from text (sometimes known as scraping)—e.g., locating all URLs in a web page. [Though, tools like BeautifulSoup, XPath and lxml are preferred for scraping.] b. Clean data—for example, removing data that's not required, removing duplicate data, handling incomplete data, fixing typos, ensuring consistent data formats, dealing with outliers and more. c. Transform data into other formats—for example, reformatting data that was collected as tab-separated or space-separated values into comma-separated values (CSV) format. d. All of the above statements are true

Answer: d

Consider the following code: In [1]: s1 = 'happy' In [2]: s2 = 'birthday In [3]: s1 += ' ' + s2 In [4]: s1 Out[4]: 'happy birthday' In [5]: symbol = '>' In [6]: symbol *= 5 In [7]: symbol Out[7]: '>>>>>' Which snippet(s) in this interactive session appear to modify existing strings, but actually create new string objects? a. Only snippet [3]. b. Only snippet [5]. c. Both snippets [5] and [6]. d. Both snippets [3] and [6]

Answer: d.

Which of the following statements a), b) or c) is false? a. A format string may contain multiple placeholders, in which case the format method's arguments correspond to the placeholders from left to right: '{} {}'.format('Amanda', 'Cyan') b. The format string can reference specific arguments by their position in the format method's argument list, starting with position 0, as in: '{0} {0} {1}'.format('Happy', 'Birthday') You can reference each argument as often as you like and in any order. c. You can reference keyword arguments by their keys in the placeholders, as in: '{first} {last}'.format(first='Amanda', last='Gray') '{last} {first}'.format(first='Amanda', last='Gray') d. All of the above statements are true.

Answer: d.

Which of the following statements a), b) or c) is false? a. A regular expression string describes a search pattern for matching characters in other strings. b. Regular expressions can help you extract data from unstructured text, such as social media posts. c. Regular expressions are also important for ensuring that data is in the correct format before you attempt to process it. d. All of the above statements are true.

Answer: d.

Which of the following statements a), b) or c) is false? a. For extremely large and small values of floating-point and Decimal types, exponential (scientific) notation can be used to format the values more compactly. b. The following interactive session shows the difference between f and e for a large value, each with three digits of precision to the right of the decimal point:In [1]: from decimal import Decimal In [2]: f'{Decimal("10000000000000000000000000.0"):.3f}' Out[2]: '10000000000000000000000000.000' In [3]: f'{Decimal("10000000000000000000000000.0"):.3e}' Out[3]: '1.000e+25' c. For the e presentation type in snippet [3] of Part (c), the formatted value 1.000e+25 is equivalent to 1.000 x 1025. If you prefer a capital E for the exponent, use the E presentation type rather than e. d. All of the above statements are true.

Answer: d.

Which of the following statements a), b) or c) is false? a. String method partition splits a string into a tuple of three strings based on the method's separator argument. The three strings are the part of the original string before the separator, the separator itself, and the part of the string after the separator. b. Consider a string representing a student's name and grades: 'Amanda: 89, 97, 92' The following code splits the original string into the student's name, the separator ': ' and a string representing the list of grades: 'Amanda: 89, 97, 92'.partition(': ') c. To search for the separator from the end of the string instead, use method rpartition to split. For example, consider the following URL string: url = 'http://www.deitel.com/books/PyCDS/table_of_contents.html' The following call to rpartition splits 'table_of_contents.html' from the rest of the URL: rest_of_url, separator, document = url.rpartition('/') d. All of the above statements are true.

Answer: d.

Which of the following statements a), b) or c) is false? a. The re module's split function tokenizes a string, using a regular expression to specify the delimiter, and returns a list of strings. b. The following code tokenizes a string by splitting it at any comma that's followed by 0 or more whitespace characters—\s is the whitespace character class and * indicates zero or more occurrences of the preceding subexpression: re.split(r',\s*', '1, 2, 3,4, 5,6,7,8') c. The following code uses the keyword argument maxsplit to specify the maximum number of splits (in this case, after the 3 splits, the fourth string contains the rest of the original string): re.split(r',\s*', '1, 2, 3,4, 5,6,7,8', maxsplit=3) d. All of the above statements are true.

Answer: d.

Which of the following statements a), b) or c) is false? a. When you read a sentence, your brain breaks it into individual words, or tokens, each of which conveys meaning. b. Interpreters like IPython tokenize statements, breaking them into individual components such as keywords, identifiers, operators and other elements of a programming language c. Tokens typically are separated by whitespace characters such as blanks, tabs and newlines, though other characters may be used—the separators are known as delimiters. d. All of the above statements are true.

Answer: d.

: Which of the following statements is false? a. By default, the following f-strings right-align the numeric values 27 and 3.5 and left-align the string "hello": f'[{27:10d}]' f'[{3.5:10f}]' f'[{"hello":10}]' b. Python formats float values with six digits of precision to the right of the decimal point by default. c. For formatted values that have fewer characters than the field width, the remaining character positions are filled with spaces. d. Formatted values with more characters than the field width cause a ValueError.

Answer: d. Actually, formatted values with more characters than the field width use as many character positions as they need

Which of the following statements is false? a. Backslash characters in strings introduce escape sequences—like \n for newline and \t for tab. b. If you wish to include a backslash in a string, you can use two back-slash characters \\. c. Raw strings—preceded by the character r—treat each backslash as a regular character, rather than the beginning of an escape sequence. d. To make your code more readable, avoid using raw strings with regular expressions.

Answer: d. Actually, raw strings can make your code more readable, particularly for regular expressions or Windows file paths like 'C:\\MyFolder\\MySubFolder\\MyFile.txt'

.Which of the following statements is false? a. The regular-expression quantifiers * and + are greedy—they match as many characters as possible. The regular expression [A-Z][a-z]+ matches 'Al', 'Eva', 'Samantha', 'Benjamin' and any other words that begin with a capital letter followed at least one lowercase letter. b. The ? quantifier matches zero or one occurrences of a subexpression. c. The regular expression \d{3,} matches strings containing at least three digits. d. You can match between n and m (exclusive) occurrences of a subexpression with the {n,m} quantifier. The regular expression \d{3,6} matches strings containing 3 to 5 digits. .

Answer: d. Actually, the given regular expression matches strings containing 3 to 6 digits, the value of m is included in the range

Based on the string sentence = '\t \n This is a test string. \t\t \n' which of the following statements is false? a. There are several string methods for removing whitespace from the ends of a string. Because strings are immutable each returns a new string leaving the original unmodified. b. The following code uses string method strip to remove the leading and trailing whitespace from sentence: sentence.strip() c. The following code snippets first use method lstrip to remove only leading whitespace from sentence: sentence.lstrip() then use method rstrip to remove only trailing whitespace: sentence.rstrip() d. Methods strip, lstrip and rstrip remove only leading and/or trailing spaces.

Answer: d. Actually, these methods remove all kinds of whitespace, including spaces, newlines and tabs