Loops, Lists, Dictionaries

The following examples show you how to manipulate files further using for loops, list comprehension and dictionaries.

For Loops

For loops help iterate over data in lists and files.

Syntax	Description
for item in sequence:	Loops through items in a sequence (list, string, etc.).
for i in range(start, stop, step):	Loops a specific number of times, from start to stop.

Example:

# Loop through a list
names = ["Alice", "Bob", "Charlie"]
for name in names:
    print(name)  # Prints each name in the list

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List Comprehension

List comprehensions allow you to create new lists from existing ones, often in a single line.

Syntax	Description
[expression for item in iterable]	Creates a list with an expression applied to each item in the iterable.
[expression for item in iterable if condition]	Creates a list with a conditional check.

Examples:

# List comprehension to create a new list with items in uppercase
names = ["Alice", "Bob", "Charlie"]
uppercase_names = [name.upper() for name in names]  
print(uppercase_names)  # ['ALICE', 'BOB', 'CHARLIE']

# List comprehension with condition (only names longer than 3 characters)
long_names = [name for name in names if len(name) > 3]
print(long_names)  # ['Alice', 'Charlie']

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Dictionaries

Dictionaries store data as key-value pairs. Useful for mapping relationships, like student names to ages.

Syntax	Description
dict = {key1: value1, key2: value2}	Creates a dictionary with key-value pairs.
dict[key]	Accesses the value associated with a key.
dict[key] = value	Adds or updates a key-value pair in the dictionary.
.items()	Returns the dictionary as key-value pairs.
.keys()	Returns the keys from the dictionary.
.values()	Returns the values from the dictionary.

Example:

# Creating a dictionary of students
student_dict = {"Alice": 15, "Bob": 14, "Charlie": 16}
print(student_dict["Alice"])  # Prints 15 (Alice's age)

Iterating Over Dictionaries

To loop through a dictionary, you can use for loops with .items(), .keys(), or .values().

Example:

# Iterate through key-value pairs
for name, age in student_dict.items():
    print(f"{name} is {age} years old")