8.3: Searching/Testing Strings
- Page ID
- 117573
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- Use the
inoperator to identify whether a given string contains a substring. - Call the
count()method to count the number of substrings in a given string. - Search a string to find a substring using the
find()method. - Use the
index()method to find the index of the first occurrence of a substring in a given string. - Write a for loop on strings using in operator.
in operator
The in Boolean operator can be used to check if a string contains another string. in returns True if the first string exists in the second string, False otherwise.
What is the output of ("a" in "an umbrella")?
2FalseTrue1
- Answer
-
c. Since
"a"is a substring of"an umbrella", the output of"a"in"an umbrella"isTrue.
What is the output of ("ab" in "arbitrary")?
TrueFalse
- Answer
-
b.
"ab"is not a substring of"arbitrary"; hence, the output isFalse.
What is the output of ("" in "string")?
TrueFalse
- Answer
-
a. Since
""is a substring of length 0 for"string", the output isTrue.
For loop using in operator
The in operator can be used to iterate over characters in a string using a for loop. In each for loop iteration, one character is read and will be the loop variable for that iteration.
What is the output of the following code?
for c in "string":
print(c, end = "")
-
string
-
s t r i n g
-
s t r i n g
- Answer
-
a. The
forloop iterates through the characters in"string"and prints all character without any separator character.
What is the output of the following code?
count = 0
for c in "abca":
if c == "a":
count += 1
print(count)
012
- Answer
-
c. The given code iterates over characters in string
"abca", and each time character"a"is observed, a counter variable is increased by 1. Since"a"appears twice in"abca", the output will be2.
What is the output of the following code?
word = "cab"
for i in word:
if i == "a":
print("A", end = "")
if i == "b":
print("B", end = "")
if i == "c":
print("C", end = "")
cababcCABABC
- Answer
-
c. The code iterates over the characters in
"cab"and prints each character's uppercase equivalent. Therefore, the output is"CAB"
count()
The count() method counts the number of occurrences of a substring in a given string. If the given substring does not exist in the given string, the value 0 is returned.
What is the output of (aaa".count("a"))?
True13
- Answer
-
c.
"aaa".count("a")returns3, which is the number of occurrences of"a"in string"aaa".
What is the output of ("weather".count("b"))?
0-1False
- Answer
-
a. Zero occurrence of
"b"exists in"weather"; hence, the output of"weather".count("b")is0.
What is the output of ("aaa".count("aa"))?
123
- Answer
-
b. Two substrings
"aa"exist in"aaa", one starting from index 0 and one starting from index 1.
find()
The find() method returns the index of the first occurrence of a substring in a given string. If the substring does not exist in the given string, the value of -1 is returned.
What is the output of "banana".find("a")?
135
- Answer
-
a. The
find()method returns the index for the first occurrence of the substring in the given string. The index for the first occurrence of"a"is 1.
What is the output of "banana".find("c")?
0-1ValueError
- Answer
-
b. Since
"c"is not a substring in"banana", thefind()method returns-1.
What is the output of "b".find("banana")?
-10ValueError
- Answer
-
a. Since
"banana"is not a substring of"b",-1is returned.
index()
The index() method performs similarly to the find() method in which the method returns the index of the first occurrence of a substring in a given string. The index() method assumes that the substring exists in the given string; otherwise, throws a ValueError.
Consider a time value is given as part of a string using the format of "hh:mm" with "hh" representing the hour and "mm" representing the minutes. To retrieve only the string's minute portion, the following code can be used:
time_string = "The time is 12:50"
index = time_string.index(":")
print(time_string[index+1:index+3])
The above code's output is:
50
What is the output of "school".index("o")?
34-3
- Answer
-
a. The
index()method returns the index of the start of the first occurrence of a substring in the given string. The index of the first occurrence of"o"in"school"is 3.
What is the output of "school".index("ooo")?
34ValueError
- Answer
-
c. Substring
"ooo"does not exist in the string"ooo"and hence theindex()method returns aValueError.
What is the output of the following code?
sentence = "This is a sentence"
index = sentence.index(" ")
print(sentence[:index])
"This""This ""sentence"
- Answer
-
a.
sentence.index(" ")returns the index of the first space character. The print statement prints the prefix of the sentence ending just before the first space character, so the output is"This".
Write a program that, given a string, counts the number of space characters in the string. Also, print the given string with all spaces removed.
Input: "This is great"
Prints:
2
Thisisgreat
Interactive Code
- Answer
-
s = "This is great"print(s.count(" "))
output = ""
for c in s:
if c != " ":
output += cprint(output)