Here are the most important Python functions to learn and master:

## Built-in Functions
1. **print()** - Output text and variables
2. **input()** - Capture user input
3. **len()** - Get the length of objects (strings, lists, etc.)
4. **range()** - Generate sequences of numbers
5. **type()** - Check the data type of an object
6. **int(), float(), str(), bool()** - Type conversion functions
7. **sum(), min(), max()** - Mathematical operations on iterables

## String Methods
1. **split()** - Convert string to list
2. **join()** - Combine list elements into string
3. **strip()** - Remove whitespace
4. **replace()** - Substitute text
5. **upper(), lower()** - Change case

## List Methods
1. **append()** - Add item to end
2. **extend()** - Add multiple items
3. **insert()** - Add item at specific position
4. **remove()** - Delete by value
5. **pop()** - Remove by index

## Dictionary Methods
1. **get()** - Retrieve value safely
2. **keys(), values(), items()** - Access dictionary components
3. **update()** - Merge dictionaries

## File Operations
1. **open()** - Access files
2. **read(), write()** - File I/O operations
3. **with** statement (context manager)

## From Standard Libraries
1. **datetime.datetime()** - Date/time handling
2. **random.randint(), random.choice()** - Generate random values
3. **os.path.join()** - File path manipulation
4. **json.loads(), json.dumps()** - JSON processing
5. **re.search(), re.findall()** - Regular expressions

## From Third-Party Libraries
1. **pandas.DataFrame()** - Data analysis
2. **numpy.array()** - Numerical computing
3. **matplotlib.pyplot.plot()** - Data visualization

Mastering these functions will give you a solid foundation for most Python programming tasks.