index in string

---

examples/strings/index.py

text = "The black cat climbed the green tree."
print(text.index("bl"))     # 4
print(text.index("The"))    # 0
print(text.index("the"))    # 22
print(text.index("dog"))

4
0
22
Traceback (most recent call last):
  File "index.py", line 5, in <module>
    print(text.index("dog"))
ValueError: substring not found