Learn Searching and Measuring

Once you can read pieces of a string, the next step is to ask questions about its contents: "does it contain this?", "where is it?", "how many times?", "does it start/end with…?".

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Use in to check if a substring appears anywhere in a string. It returns a Boolean.


              123
            
s = "Python programming"
print("gram" in s)      # True
print("Java" not in s)  # True

Finding Positions

find(sub) returns the starting index of the first match, or -1 if not found;
rfind(sub) searches from the right and returns the last match index (or -1);
index(sub) is like find, but raises ValueError if the substring is missing.


              12345
            
s = "abracadabra"
print(s.find("bra"))    # 1
print(s.rfind("bra"))   # 8
print(s.find("xyz"))    # -1
print(s.index("xyz"))   # ValueError

Counting Occurrences

count(sub) returns how many non-overlapping times the substring appears.


              123
            
s = "banana"
print(s.count("a"))     # 3
print(s.count("na"))    # 2

Starts and Ends

To check a string's start or end, use startswith or endswith; these are clearer and safer than slicing when you only need a yes/no answer.


              123
            
fname = "report_final.pdf"
print(fname.startswith("report"))  # True
print(fname.endswith(".pdf"))      # True

Case-insensitive checks (simple and practical)

String methods are case-sensitive. For case-insensitive search, normalize both sides with .lower() (or .upper()).


              123
            
msg = "Hello, World!"
print("hello" in msg.lower())          # True
print(msg.lower().startswith("hello")) # True

Note

We already used len() in the previous chapter to measure length; here we focus on content checks and locations.

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Section 3. Chapter 3

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Once you can read pieces of a string, the next step is to ask questions about its contents: "does it contain this?", "where is it?", "how many times?", "does it start/end with…?".

Membership

Use in to check if a substring appears anywhere in a string. It returns a Boolean.


              123
            
s = "Python programming"
print("gram" in s)      # True
print("Java" not in s)  # True

Finding Positions

find(sub) returns the starting index of the first match, or -1 if not found;
rfind(sub) searches from the right and returns the last match index (or -1);
index(sub) is like find, but raises ValueError if the substring is missing.


              12345
            
s = "abracadabra"
print(s.find("bra"))    # 1
print(s.rfind("bra"))   # 8
print(s.find("xyz"))    # -1
print(s.index("xyz"))   # ValueError

Counting Occurrences

count(sub) returns how many non-overlapping times the substring appears.


              123
            
s = "banana"
print(s.count("a"))     # 3
print(s.count("na"))    # 2

Starts and Ends

To check a string's start or end, use startswith or endswith; these are clearer and safer than slicing when you only need a yes/no answer.


              123
            
fname = "report_final.pdf"
print(fname.startswith("report"))  # True
print(fname.endswith(".pdf"))      # True

Case-insensitive checks (simple and practical)

String methods are case-sensitive. For case-insensitive search, normalize both sides with .lower() (or .upper()).


              123
            
msg = "Hello, World!"
print("hello" in msg.lower())          # True
print(msg.lower().startswith("hello")) # True

Note

We already used len() in the previous chapter to measure length; here we focus on content checks and locations.

Everything was clear?

Thanks for your feedback!

Section 3. Chapter 3

Searching and Measuring

Membership

Finding Positions

Counting Occurrences

Starts and Ends

Case-insensitive checks (simple and practical)

1. What will this code output?

2. Which statement does not raise an error when the substring is missing?

3. Given `s = "Banana"`, which expression returns `True` case-insensitively for checking the prefix `"ba"`?

Awesome!

Searching and Measuring

Membership

Finding Positions

Counting Occurrences

Starts and Ends

Case-insensitive checks (simple and practical)

1. What will this code output?

2. Which statement does not raise an error when the substring is missing?

3. Given `s = "Banana"`, which expression returns `True` case-insensitively for checking the prefix `"ba"`?

Searching and Measuring

Membership

Finding Positions

Counting Occurrences

Starts and Ends

Case-insensitive checks (simple and practical)

1. What will this code output?

2. Which statement does not raise an error when the substring is missing?

3. Given s = "Banana", which expression returns True case-insensitively for checking the prefix "ba"?

Awesome!

Searching and Measuring

Membership

Finding Positions

Counting Occurrences

Starts and Ends

Case-insensitive checks (simple and practical)

1. What will this code output?

2. Which statement does not raise an error when the substring is missing?

3. Given s = "Banana", which expression returns True case-insensitively for checking the prefix "ba"?

3. Given `s = "Banana"`, which expression returns `True` case-insensitively for checking the prefix `"ba"`?

3. Given `s = "Banana"`, which expression returns `True` case-insensitively for checking the prefix `"ba"`?