Call math.sqrt() to compute real square roots in Python. For negative or complex inputs, switch to cmath.sqrt(). When you need elementwise roots over arrays, use numpy.sqrt(); for integer-only results (floor of the root), use math.isqrt().

Method 1 — Use math.sqrt() for real, non-negative numbers

Import the standard math module.

import math

Call math.sqrt(x) with an int or float to get a float result.

math.sqrt(49)      # 7.0
math.sqrt(70.5)    # 8.396427811873332
math.sqrt(0)       # 0.0

Handle negative inputs; math.sqrt raises ValueError for x < 0.

def safe_sqrt(x):
    import math
    try:
        return math.sqrt(x)
    except ValueError:
        return "Use cmath.sqrt() for negatives."

Apply to a real-world calculation (Pythagorean theorem).

a, b = 27, 39
run_distance = math.sqrt(a**2 + b**2)  # 47.43416490252569

Method 2 — Use cmath.sqrt() for negative or complex inputs

Import cmath for complex-number support.

import cmath

Call cmath.sqrt(x) for negatives or complex numbers; it always returns a complex value.

cmath.sqrt(-25)     # 5j
cmath.sqrt(8j)       # (2+2j)

Access components via result.real and result.imag if needed.

z = cmath.sqrt(-4)
z.real, z.imag      # (0.0, 2.0)

Method 3 — Use NumPy for vectorized square roots over arrays

Import NumPy.

import numpy as np

Compute elementwise roots with np.sqrt; pass arrays or scalars.

arr = np.array([4, 9, 16, 25])
np.sqrt(arr)        # array([2., 3., 4., 5.])

Handle negatives: np.sqrt gives nan for negative reals; use np.emath.sqrt() or cast to complex.

a = np.array([4, -1, np.inf])
np.sqrt(a)              # [ 2., nan, inf]
np.emath.sqrt(a)        # [ 2.+0.j,  0.+1.j, inf+0.j]
np.sqrt(a.astype(complex))  # [ 2.+0.j,  0.+1.j, inf+0.j]

Method 4 — Use the exponent operator or pow() when you cannot import a module

Raise to the power of one-half with the power operator.

9 ** 0.5     # 3.0
2 ** 0.5     # 1.4142135623730951

Respect precedence for negatives; parentheses are required to avoid applying unary minus after exponentiation.

-4 ** 0.5      # -2.0  (interpreted as -(4 ** 0.5))
(-4) ** 0.5    # (1.2246467991473532e-16+2j)  complex result

Alternatively, use pow(x, 0.5) for the same effect on non-negative inputs.

pow(16, 0.5)   # 4.0

Method 5 — Get integer square roots (floor) for exact integer math

Use math.isqrt(n) to get the integer square root (floor) of a non-negative integer.

import math
math.isqrt(10)   # 3  (since 3*3 = 9 ≤ 10 < 4*4)

Check perfect squares with a single comparison.

n = 49
r = math.isqrt(n)
is_perfect_square = (r * r == n)   # True

Notes and pitfalls

math.sqrt() works for real, non-negative inputs and returns a float; zero is valid.
Negative inputs need cmath.sqrt() to obtain a complex result.
numpy.sqrt() is vectorized and fast for arrays; negative real values produce nan unless you use np.emath.sqrt() or complex dtype.
The exponent operator ** and pow() can compute square roots but are less explicit; prefer math.sqrt() for readability and typically better speed.
Floating-point results can be inexact for very large integers; use math.isqrt() for exact integer-floor results.

Pick math.sqrt() for standard real inputs, cmath.sqrt() for negatives/complex values, and numpy.sqrt() when you need vectorized operations; use math.isqrt() for exact integer floors.