Python timeit() – Measuring Execution Time with Practical Examples

What is Python timeit()?

Python timeit() is a built‑in module designed to measure the execution time of small code snippets with high precision. By default it runs the statement one million times and reports the fastest run, which helps you compare performance of different implementations.

Syntax

timeit.timeit(stmt, setup, timer, number)

Parameters

• stmt – The code to time. Default is pass.
• setup – Code that runs once before stmt. Default is pass.
• timer – Optional timer function. The module supplies a suitable default.
• number – How many times stmt is executed. Default is 1 000 000.

Import the module first:

import timeit

Example 1 – Timing a Simple Expression

# Test a basic arithmetic operation import timeit print(timeit.timeit("output = 10*5"))

Typical output:

0.06127880399999999

This shows the time (in seconds) taken for the fastest of one million runs.

Timing Multiple Lines

timeit can handle multi‑line code by separating statements with semicolons or by passing a triple‑quoted string.

Using Semicolons

import timeit
print("The time taken is ", timeit.timeit(stmt="a=10;b=10;sum=a+b"))

Output:

The time taken is  0.137031482

Using Triple‑Quoted Strings

import timeit
import_module = "import random"
testcode = ''' 
def test(): 
    return random.randint(10, 100)
'''
print(timeit.repeat(stmt=testcode, setup=import_module))

Output:

C:\pythontest>python testtimeit.py
The time taken is  0.182619178

Key Methods

• timeit.default_timer() – Returns the current time with the best available resolution.
• timeit.repeat(stmt, setup, timer, repeat, number) – Runs timeit() repeatedly, returning a list of best times for each run.

Example 1 – Using timeit.timeit()

# Test a function that returns a random integer
import timeit
import_module = "import random"
testcode = ''' 
def test(): 
    return random.randint(10, 100)
'''
print(timeit.timeit(stmt=testcode, setup=import_module))

Output:

0.46715912400000004

Example 2 – Using default_timer()

# Measure a single function call
import timeit
import random

def test():
    return random.randint(10, 100)

starttime = timeit.default_timer()
print("The start time is :", starttime)
test()
print("The time difference is :", timeit.default_timer() - starttime)

Output:

The start time is : 0.220261875
The time difference is : 0.0004737320000000045

Example 3 – Using timeit.repeat()

# Run the test five times and capture the best times
import timeit
import_module = "import random"
testcode = ''' 
def test(): 
    return random.randint(10, 100)
'''
print(timeit.repeat(stmt=testcode, setup=import_module, repeat=5))

Output:

[0.43638873, 0.5040939680000001, 0.5069179909999999, 0.3943449330000002, 0.3546886979999999]

Each entry is the best time for one iteration of the 1 000 000 runs.

Command‑Line Usage

You can invoke timeit directly from the shell:

python -m timeit [-n N] [-r N] [-s S] [-t] [-c] [-h] [code statement ...]

• -n N – Number of loops for the statement.
• -r N – How many times the entire timing process repeats.
• -s S – Setup code executed once before timing.
• -t – Use time.time() as the timer.
• -c – Use time.clock() as the timer.
• -h – Show help.

Example

C:\pythontest>python -m timeit -s 'text="hello world"'
20000000 loops, best of 5: 13.1 nsec per loop

Another convenient way is to call timeit from the REPL:

import timeit
print("The time taken is ", timeit.timeit(stmt="a=10;b=10;sum=a+b"))

Output:

The time taken is  0.15048536300000137

Why timeit() is the Best Tool for Timing Python Code

• It runs the statement many times (default 1 000 000) and returns the fastest run, giving a reliable estimate.
• Garbage collection is disabled during timing, preventing it from skewing results.
• It automatically selects the most precise timer for your operating system (e.g., time.clock() on Windows, time.time() on macOS/Linux).

Summary

The timeit module is essential for benchmarking short Python snippets. Its parameters are straightforward:

• stmt – Code to time.
• setup – One‑time setup code.
• timer – Optional timer function.
• number – How many times stmt runs.

Make sure to use timeit for accurate, repeatable measurements.