Understanding Strings: The Building Blocks of Text in Python

Welcome to Episode 7 of The Medical Coder’s Path!

In Episode 6, we introduced Python data types and provided a general overview of collections like lists, tuples, and dictionaries. Now, in Episode 7, we’ll begin exploring each data type one by one, starting with Strings.

🎯 Objective

By the end of this episode, learners will understand:

• What a string is in Python.

• How to create and store strings.

• The len() Function in Python

• Common string operations (concatenation, indexing, and slicing).

Let’s get started!

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What a string is in Python

In Python, a string is a sequence of characters, which can include letters, numbers, or symbols, enclosed in either single quotes ('...') or double quotes ("..."). These quotes are known as delimiters. A delimiter is a character that indicates where a string begins and ends in Python.

📌 Example (healthcare context):

patient_name = "Ahmed Ali"
diagnosis = "Hypertension"
hospital_id = "CH12345"
hospital = 'City Hospital'

Python can tell us what kind of data we’re dealing with by using the type() function.

Example:

patient_name = "Ahmed Ali"
print(type(patient_name))

Output:

<class 'str'>

This shows that the variable patient_name is of the type string (str).

Strings vs. String Literals

• String: In Python, a string is a data type used to represent text. When we call something a string, it means the stored value is text.
  String literal: This refers to the exact characters you write in your code to create a string. For example, "Mohamed Omer" is a string literal, the quotes and text you type. When stored in a variable, like patient_name = "Mohamed Omer", the value of patient_name is a string.

👉 In short:

String Literal → "Mohamed Omer"  (what you write in code with quotes)
String         → Mohamed Omer    (the actual stored text)

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The len() Function in Python

In Python, the len() function is used to find the length of a string, which is the total number of characters it contains, including spaces and symbols.

This is very useful in healthcare settings, for example, when checking if a patient ID or medical record number has the correct length.

🩺 Example 1: Simple String

patient_name = "Ahmed Ali"
print(len(patient_name))

Output:

9

👉 The string "Ahmed Ali" has 9 characters (including the space between Ahmed and Ali).

🩺 Example 2: Patient ID

patient_id = "MRN12345"
print(len(patient_id))

Output:

8

👉 The patient ID has 8 characters, which can be checked to ensure it matches the required format.

🩺 Example 3: Empty String

note = ""
print(len(note))

Output:

0

👉 An empty string has a length of 0.

✅ Key Takeaway:

• len() counts every character, including spaces, numbers, and symbols.

• It helps you validate input (e.g., ensuring a password, patient ID, or report isn’t too short or too long).

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Multiline Strings in Python

Sometimes, a single line of text is not enough. In healthcare or medical informatics, you may want to store long notes, discharge summaries, or patient history that spread across multiple lines.

Python allows us to create multiline strings using triple quotes (""" or ''').

🩺 Example 1: Patient Note

patient_note = """Patient complains of headache.
Blood pressure measured at 140/90.
Advised to reduce salt intake and follow up in 2 weeks."""
print(patient_note)

Output:

Patient complains of headache.
Blood pressure measured at 140/90.
Advised to reduce salt intake and follow up in 2 weeks.

👉 Notice how the text keeps its format across multiple lines.

🩺 Example 2: Medical Report (with triple single quotes)

medical_report = '''Lab results:
- Hemoglobin: 13.5 g/dL
- Glucose: 95 mg/dL
- Cholesterol: Normal
'''
print(medical_report)

Output:

Lab results:
- Hemoglobin: 13.5 g/dL
- Glucose: 95 mg/dL
- Cholesterol: Normal

✅ Key Notes on Multiline Strings

• They are defined with triple quotes (""" or ''').

• Useful for storing paragraphs, reports, or formatted text.

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String Operations

1️⃣ Concatenation (Joining strings together)

Concatenation means combining two or more strings into one. This is very useful in healthcare when you want to join patient information, like their name and ID, into a single message, using the + operator.

single message.

first_name = "Ahmed"
last_name = "Ali"
full_name = first_name + " " + last_name # The purpose of the double quotes here is to create a space between the two names. 
print(full_name)

Output:

Ahmed Ali

2️⃣ Repetition (Repeating a string)

Repetition allows you to repeat a string multiple times using the * operator. This can be helpful, for example, when creating separators in reports or repeating a symbol.

separator = "-" * 30
print(separator)

Output:

------------------------------

3️⃣ Indexing (Accessing a single character)

When you write a string in Python, Python stores it in memory as a sequence of characters. To help us find or work with specific characters, Python gives each character a numbered position, which we call an index.

Think of a string as a row of numbered lockers, where each locker holds one character.

• Indexing from Left to Right (Positive Indexing)

  In Python, when you count from the left side, indexing starts at 0 (not 1).

  For example:

word = "HELLO"

Here’s how Python sees it:

👉 That means:

• word[0] → "H"

• word[1] → "E"

• word[4] → "O"

Indexing from Right to Left (Negative Indexing)

Python also allows us to count from the right side. When we count backwards, the index starts at -1.

Using the same example:

word = "HELLO"

👉 That means:

• word[-1] → "O" (last character)

• word[-2] → "L" (second from the right)

• word[-5] → "H" (first character, same as index 0)

patient_id = "MRN12345"
print(patient_id[0])  # First character
print(patient_id[-1]) # Last character

Output:

M
5

4️⃣ Slicing (Extracting part of a string)

Slicing means cutting out a substring (a smaller piece of a string) by telling Python where to start and where to stop.

The basic syntax is:

string[start:stop]

• start → the index where the slice begins (included).

• stop → the index where the slice ends (excluded).

word = "HOSPITAL"

print(word[0:4])   # "HOSP"
print(word[2:7])   # "SPITA"

👉 Notice that the slice includes the character at the start index, but stops right before the stop index.

Output:

HOSP
SPITA

Sometimes you don’t always have to write both numbers.

• If you leave out start, Python begins at the beginning.

• If you leave out stop, Python goes all the way to the end.

print(word[:4])   # "HOSP"   (from start to index 3)
print(word[3:])   # "PITAL"  (from index 3 to end)
print(word[:])    # "HOSPITAL" (entire string)

You can also slice from the right using negative indexes.

print(word[-4:])   # "ITAL"  (last 4 letters)
print(word[:-3])   # "HOSPI" (everything except last 3)

There’s an optional step value:

string[start:stop:step]

• step tells Python how many characters to skip.

print(word[0:7:2])   # "HSPL" (every 2nd character)
print(word[::-1])    # "LATIPSOH" (reverses the string)

Slicing is like cutting out a piece of a cake; it always includes the start index but stops right before the stop index. You can use positive or negative indices, and you can also add a step to skip characters or reverse a string.

5️⃣ Membership (Checking if a word exists in a string)

You can use the keywords in or not in to check if a substring exists inside a string.

note = "Patient has diabetes"
print("diabetes" in note)     # True
print("cancer" not in note)   # True

Output:

True
True

These are the basic string operations. Later, we can also explore string methods (like .lower(), .upper(), .replace(), etc.) which make working with strings even more powerful.

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Let’s wrap up Episode 7 with a hands-on exercise!

📝 Practice Exercise: Strings in Action

You are given this string:

patient_name = "Samar Ali"

Part 1: Indexing

1. Print the first character of the name.

2. Print the last character of the name.

Part 2: Slicing

3. Extract "Samar" from the string.

4. Extract "Ali" from the string.

5. Reverse the entire string.

6. Get every second letter in "Samar".

Part 3: String Operations

7. Concatenate " Samar Ali" with the string " is a patient".

8. Repeat the string "ID-" 3 times.

9. Find the length of the string using len()

After you finish, send your answers to my email saja@sajamedtech.com for feedback.

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What’s Next?

In the next episode, we’ll explore string methods in Python that allow us to transform, clean, and analyze text data more effectively.

See You Later!