[Python] How to Use IPython Magic Commands (Magic Functions)

IPython provides a set of convenient commands called “Magic Functions” for measuring code execution time or manipulating external files. These are executed by prefixing them with %.

List of Main Magic Commands

Magic Function	Role	Parameter Example
%timeit	Measures execution time of code (calculates average over multiple runs).	%timeit range(100)
%run	Executes an external Python script file.	%run script.py
%history	Displays input history so far.	%history -n 1-5
%save	Saves history of specified lines to a file.	%save file.py 1-10
%load	Loads code from an external file into the current input cell.	%load script.py
%pwd	Displays the current working directory (path).	%pwd
%ls	Displays a list of files in the current directory.	%ls

Execution Examples

1. Measuring Code Execution Time (%timeit)

Automatically loops the specified code multiple times to calculate the most accurate average execution time.

In [1]: %timeit list(range(1000))
9.85 µs ± 120 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

2. Executing External Scripts (%run)

Executes a .py file located in the current directory within the IPython environment. Variables after execution remain accessible within IPython.

sample.py (File created in advance)

print("This is a sample script.")
message = "Hello from script!"

Execution in IPython

In [2]: %run sample.py
This is a sample script.

In [3]: print(message)
Hello from script!

3. Referencing and Saving History (%history, %save)

You can check code entered in the past or select specific lines to save to a file.

# Execute some code
In [4]: s = "sample string"
In [5]: print(s)
sample string

# Check history (Display all without options)
In [6]: %history
%timeit list(range(1000))
%run sample.py
print(message)
s = "sample string"
print(s)

# Save specific lines (lines 4 and 5) to 'sample2.py'
In [7]: %save sample2.py 4 5
The following commands were written to file 'sample2.py':
s = "sample string"
print(s)

4. Loading Code (%load)

Expands the content of a file into the current cell. This is convenient when you want to check or edit the content before execution.

In [8]: %load sample2.py

# When executed, the cell content changes as follows:
# %load sample2.py
s = "sample string"
print(s)

Supplement: Line Magic and Cell Magic

• Line Magic (%): Commands effective for a single line. (Example: %timeit)
• Cell Magic (%%): Commands effective for the entire cell. (Example: Writing %%timeit measures the time for the entire multi-line code in that cell.)