Functions in Python

Functions in Python are blocks of reusable code that carry out a specific task. When working on larger scale projects, functions provide better modularity for your application and a high degree of code reusing.

Python has many built-in functions like print(), input(), len(), etc, but you can also create your own functions. These functions are called user-defined functions.

Defining a Function

You can define your own function in Python using the keyword def.

Here’s a simple example of a function that calculates the square of a number:

def square(number):
    sq = number ** 2
    return sq

In this code, square is the function name, number is the input parameter to the function, the operator ** is used to calculate the square of a number and return is the keyword used to output a value from the function.

Calling a Function

To call a function, you simply need to provide the function name followed by parentheses with required parameters, if any.

print(square(6)) #Output: 36

Function Parameters

You can pass data, known as parameters, into a function. A function can accept any number and type of parameters.

Let’s create a function that greet a user:

def greet(name):
    print("Hello, " + name + ". Good Morning!")

Now we can call this function and pass a name as the argument:

greet('Alice') #Output: Hello, Alice. Good Morning!

Using Default Parameter Value

You can set a default parameter value for a function. If we call the function without argument, it uses the default value.

def greet(name = "User"):
    print("Hello, " + name + ". Good Morning!") 

greet() #Output: Hello, User. Good Morning!

In the context of chemistry, we can wrap a series of calculations within a function. For example, a chemist may often need to calculate the molar mass for different substances. This can be done using a function:

# Function to calculate molar mass of hydrocarbons
def calculate_molar_mass(hydrogen, carbon):
    H = 1.008  # molar mass of Hydrogen
    C = 12.01  # molar mass of Carbon
    return (H*hydrogen + C*carbon)

# Now calculate molar mass of Methane (CH4)
print(calculate_molar_mass(4, 1))  #Output: 16.042

This way, chemists can create their own library of useful functions to perform various calculations related to their work, increasing efficiency and reducing the chance of errors in their calculations.

Examples of Functions in Python

Let’s go through more examples of functions, this time keeping our examples more chemistry oriented.

Calculating Amount of Substance

Say you routinely need to calculate the number of moles in a sample given its mass and molar mass. We can make a function to do exactly this:

# Function to calculate amount of substance
def calculate_moles(mass, molar_mass):
    return mass / molar_mass

# Now calculate the moles in a 22g sample of Carbon (C = 12.01 g/mol)
print(calculate_moles(22, 12.01)) 

Calculating Dilution

If you often perform dilutions, you might want a function to quickly calculate the final concentration after dilution:

# Function to calculate final concentration after dilution
def dilute(C1, V1, V2):
    return (C1 * V1) / V2

# Now calculate the concentration after dilution
print(dilute(0.5, 5, 10))  

Examples

1. Write a function to calculate the pH of a solution given the concentration of H+ ions.
2. Write a function that returns the concentration of OH- ions given the concentration of H+ ions.
3. Write a function to calculate the final pressure of a gas given initial pressure, volume and temperature, and final volume and temperature (use ideal gas law).
4. Write a function that calculates and returns the molar mass of a hydrocarbon given numbers of H, C and O atoms.
5. Write a function that calculates mass percent of an element in a compound given the molar mass of the element and the compound.

Code

Solution 1:

import math

def calculate_pH(H_concentration):
    return -math.log10(H_concentration)

print(calculate_pH(0.0001))  

Solution 2:

def calculate_OH_concentration(H_concentration):
    Kw = 1.0e-14
    return Kw / H_concentration

print(calculate_pH(0.0001))   

Solution 3:

def calculate_final_pressure(P1, V1, T1, V2, T2):
    return (P1 * V1 / T1) * (T2 / V2)

print(calculate_final_pressure(2, 10, 300, 5, 300))  

Solution 4:

def calculate_molar_mass(hydrogen, carbon, oxygen):
    H = 1.008  
    C = 12.01 
    O = 16.00 
    return (H*hydrogen + C*carbon + O*oxygen)

print(calculate_molar_mass(4, 2, 2)) 

Solution 5:

def calculate_mass_percent(element_molar_mass, compound_molar_mass):
    return (element_molar_mass / compound_molar_mass) * 100

print(calculate_mass_percent(12.01, 18.015)) 

That’s it! By writing and using your own functions, your code becomes more readable and reusable.