Python | sympy.lambdify() method

With the help of sympy.lambdify() method, we can convert a SymPy expression to an expression that can be numerically evaluated. lambdify acts like a lambda function, except it, converts the SymPy names to the names of the given numerical library, usually NumPy or math.

Syntax: lambdify(variable, expression, library)

Parameters:
variable – It is the variable in the mathematical expression.
expression – It is the mathematical expression which is converted into its respective name in the given library.
library – It is the Python library to which expression is to be converted into.

Returns: Returns a lambda function which can evaluate a mathematical expression.

Example #1:
In this example we can see that by using sympy.lambdify() method, we can get a lambda function from a mathematical expression.

# import sympy
from sympy import *

x = symbols('x')
expr = sin(x)

# Use sympy.lambdify() method
f = lambdify(x, expr, "math")

print("Using lambda function in SymPy to evaluate sin(90) : {}".format(f(90)))

Output:

Using lambda function in SymPy to evaluate sin(90) : 0.893996663601

Example #2:
We can pass a dictionary of sympy_name:numerical_function pair to use lambdify with numerical libraries that it does not know about.

# import sympy
from sympy import *

def squared(n) :
    return n**2

x = symbols('x')
expr = x**2

# Use sympy.lambdify() method
f = lambdify(x, expr, {"**" : squared})

print("Using lambda function in SymPy to evaluate squared function : {}".format(f(10)))

Output:

Using lambda function in SymPy to evaluate squared function : 100