try statements

https://docs.python.org/3/reference/compound_stmts.html#try

INTRODUCTION

The 'try' statement can be used used to specify exception handlers and/or cleanup code for a group of statements.

The 'except' clause(s) specify one or more exception handlers.

The 'finally' clause can be used to specify cleanup code which does not handle the exception, but is executed whether an exception occurred or not in the preceding code.

# Syntax.
# (1) try + except (one or more) + else (optional) + finally (optional)
# (2) try + finally

try:
    statements
except ExceptionClass1:   # matching ExceptionClass1
    statements
except (ExceptionClass2, ExceptionClass3):   # matching two exception classes
    statements
except ExceptionClass4 as exception1:   # exception1 is an instance
    statements
except (ExceptionClass4, ExceptionClass5) as exception2:
    statements
#except:   # if present, must be the last; it matches any exception
except Exception:   # recommended
    statements
else:   # optional, executed if no exception was raised
    statements
finally:   # if present, it is always executed
    statements

L = []
# L = [1, 2, 3]
try:
    print(L[1])
except IndexError:
    print("exception is present")
else:
    print("no exception")
print("after try")

afile = open("book.txt")
try:        # working with the file
    text = afile.read()   # reading the file
finally:   # the file will always be closed
    afile.close()
print("after try")
# Now 'with' is recommended.

import sys

print(sys.exc_info())   # return (type, value, traceback)
# Return information about the most recent exception caught by an except
# clause in the current stack frame or in an older stack frame.

EXAMPLES

# Py2 and Py3 compatibility.
try:
    input = raw_input   # input() in Py2 is slow and dangerous
except NameError:   # we are in Py3
    pass

# Py2 and Py3 compatibility.
try:
    integer_types = (int, long)
except NameError:   # we are in Py3
    integer_types = (int,)
# Usage: isinstance(variable, integer_types)

# Interactions with users.
while True:
    reply = input("Enter int: ")   # Py3
    try:
        value = int(reply)
    except ValueError:
        print("This is not int!")
    else:
        break
print("value is set to {}".format(value))