Hello world in Qiskit

qello_world.py

from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister
from math import sqrt

psi = [1/sqrt(2), 1/sqrt(2)]

def prepare(qc, psi):
    qc.initialize(psi, [0])     # [0] indicates the zeroth index (or) the first qubit

# State preparation
###########################
qr = QuantumRegister(1)
cr = ClassicalRegister(1)

qc = QuantumCircuit(qr, cr)
prepare(qc, psi)

qc.measure(qr[0], cr[0])

# Measurement
###########################
from qiskit import Aer, transpile
backend = Aer.get_backend('qasm_simulator')

qc_compiled = transpile(qc, backend)

job = backend.run(qc_compiled, shots=1024)
results = job.result()

counts = results.get_counts(qc_compiled)

# Visualization
###########################
from qiskit.visualization import plot_histogram
plot_histogram(counts)