PCAP Strings Practice Test 1 — 15 Questions

Question 1

A programmer writes a function to check if a string is a palindrome (ignoring case and non-alphanumeric characters). Which implementation correctly achieves this?

Accepted Answer

def is_pal(s): s = ''.join(c for c in s if c.isalnum()).lower(); return s == s[::-1]. It first filters the string to keep only alphanumeric characters using `c.isalnum()`, converts the result to lowercase with `.lower()`, and then compares the string to its reverse using slicing `s[::-1]`. This correctly handles case insensitivity and ignores non-alphanumeric characters, which is the standard approach for palindrome checking in Python.

Answer

def is_pal(s): s = s.lower(); return s == ''.join(reversed(s))

Answer

def is_pal(s): return s == s[::-1]

Answer

def is_pal(s): s = s.lower(); return s == s[::-1]

Question 2

A log analysis script needs to extract all IP addresses from a string. The IPs are in dotted-decimal format. Which regex pattern will correctly extract them?

Accepted Answer

r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}'. Both B and C match four octets of 1–3 digits separated by periods and will correctly extract IPs from a string. Option A contains an erroneous space, and option D allows octets of any length. Since the question asks for a pattern that correctly extracts, both B and C are valid; a single correct answer cannot be justified.

Answer

r'[0-9]+\. [0-9]+\.[0-9]+\.[0-9]+'

Answer

r'\d+\.\d+\.\d+\.\d+'

Question 3

Which string method can be used to check if a string contains only digits?

Accepted Answer

str.isdigit(). The `str.isdigit()` method returns `True` if all characters in the string are digits (0-9) and the string is non-empty. This is the most direct and commonly used method for checking numeric-only strings in Python, as it specifically tests for digit characters without including other numeric forms like fractions or Roman numerals.

Answer

str.isalnum()

Answer

str.isdecimal()

Answer

str.isnumeric()

Question 4

A developer needs to replace all occurrences of 'cat' with 'dog' in a string, but only if 'cat' is a whole word (not part of 'category'). Which code achieves this?

Accepted Answer

re.sub(r'\bcat\b', 'dog', s). Uses the `re.sub()` function with the regex pattern `r'\bcat\b'`, where `\b` denotes a word boundary. This ensures that only the whole word 'cat' is matched and replaced with 'dog', ignoring cases where 'cat' appears as part of a larger word like 'category'. The `r` prefix makes it a raw string, preventing escape sequence issues.

Answer

s.replace('cat', 'dog')

Answer

re.sub('cat', 'dog', s)

Answer

s.replace('cat', 'dog', 1)

Question 5

Given the string s = 'Hello World!', which expression returns a list of characters?

Accepted Answer

list(s). The `list()` constructor, when passed a string, iterates over each character in the string and returns a list where each element is a single character. For `s = 'Hello World!'`, `list(s)` produces `['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '!']`, which is exactly a list of characters.

Answer

s.split('')

Answer

s.split()

Answer

s.split(' ')

Question 6

Which of the following is the correct way to format a string with variables?

Accepted Answer

f'Name: {name}, Age: {age}'. Option C uses an f-string (formatted string literal), the modern recommended way in Python 3.6+ to embed variables directly into strings. Option A uses old-style % formatting, which is syntactically correct but outdated and less readable, so it is not the best modern approach. Option B is incorrect because .format() with named placeholders like {name} requires keyword arguments (e.g., .format(name=name, age=age)); passing positional arguments without indices will raise a KeyError. Option D is incorrect because it swaps the positional indices, so it would put age in place of name and vice versa.

Answer

'Name: %s, Age: %d' % (name, age)

Answer

'Name: {name}, Age: {age}'.format(name, age)

Answer

'Name: {0}, Age: {1}'.format(age, name)

Question 7

What is the result of 'Python'.find('th')?

Accepted Answer

2. The string method `find()` returns the lowest index where the substring is found. In 'Python', the substring 'th' starts at index 2 (P=0, y=1, t=2, h=3, o=4, n=5). Therefore, the result is 2, making option C correct.

Answer

1

Answer

-1

Answer

0

Question 8

Which of the following methods can be used to check if a string starts with a vowel?

Accepted Answer

s.startswith(('a','e','i','o','u')). The `str.startswith()` method accepts a tuple of prefixes to check against. When a tuple is passed, Python checks if the string starts with any of the elements in the tuple, making it the proper way to test for multiple vowel prefixes in a single call.

Answer

s[0] in 'aeiou'

Answer

s.startswith('a','e','i','o','u')

Answer

s.startswith('a') or 'e' or 'i' or 'o' or 'u'

Question 9

Which TWO statements are true regarding strings in Python?

Accepted Answer

Strings can be concatenated with the + operator.. Strings in Python support concatenation using the + operator, which joins two or more strings into a single string. This is a fundamental operation for combining textual data, and it works by creating a new string object that contains the characters from both operands in sequence.

Answer

Strings are not sequences.

Answer

Strings are mutable.

Answer

Strings do not support indexing.

Question 10

Which THREE are valid escape sequences in Python strings?

Accepted Answer

. 
 is a standard escape sequence in Python that represents a newline character (ASCII LF, 0x0A). It is defined in the Python language specification and is commonly used to insert line breaks in string literals.

Answer

\q

Answer

\z

Question 11

Given s = 'Hello
World!

', what is the length of string s?

Accepted Answer

18. The string s = 'Hello
World!

' contains 7 newline escape sequences: one after 'Hello' and six after 'World!'. Each 
 is a single character. Counting: H(1), e(2), l(3), l(4), o(5), 
(6), W(7), o(8), r(9), l(10), d(11), !(12), then the six additional newlines (13-18). Total length = 18. A common mistake is to miscount the newline escapes or to treat 
 as two characters; if you treated all 7 
 as two characters, the length would be 25, not 19.

Answer

16

Answer

17

Answer

19

Question 12

What is the value of matches?

Accepted Answer

['Alice', 'Bob']. The `re.findall(r'[A-Z][a-z]*', 'Alice and Bob are friends')` call matches all sequences starting with an uppercase letter followed by zero or more lowercase letters. This yields 'Alice' and 'Bob', as they are the only words beginning with a capital letter. The result is a list of those two strings.

Answer

['Alice']

Answer

['Alice', 'and', 'Bob', 'are', 'friends']

Answer

['Alice', 'Bob', 'friends']

Question 13

You are a network engineer troubleshooting a script that processes router configuration files. The script reads a configuration line from a file: 'interface GigabitEthernet0/1
 ip address 192.168.1.1 255.255.255.0
 no shutdown'. The script needs to extract the interface name and IP address. The current code uses string split operations but fails when the line has extra spaces or tabs. For example, when the line is 'interface   GigabitEthernet0/1', the split returns ['interface', '', '', 'GigabitEthernet0/1'] and the script fails. You need to modify the script to robustly extract the interface name and IP address regardless of whitespace. Which approach should you take?

Accepted Answer

Use line.split() instead of line.split(' ').. `line.split()` without arguments splits on any whitespace (spaces, tabs, newlines) and automatically removes empty strings, making it robust against extra spaces or tabs. In contrast, `line.split(' ')` splits only on single space characters, leaving empty strings when multiple spaces or tabs are present. This behavior is defined by Python's string method documentation and is essential for parsing configuration files where whitespace is inconsistent.

Answer

Manually iterate and concatenate characters until a space is found.

Answer

Use line.split(' ') and then filter out empty strings.

Answer

Use line.startswith('interface') to identify the line, then extract substring.

Question 14

When processing a large text file, a developer notices that using str.replace() in a loop is slow. Which alternative is most efficient for multiple replacements?

Accepted Answer

Use str.translate() with a translation table. `str.translate()` with a translation table built by `str.maketrans()` performs all character replacements in a single pass over the string, operating at the C level in CPython. This avoids the O(n) per-replacement overhead of `str.replace()` in a loop, making it the most efficient choice for multiple, fixed-character substitutions on large text.

Answer

Use str.maketrans() on the original string

Answer

Use re.sub() from the re module

Answer

Chain multiple str.replace() calls