Exceptions in python

Exceptions in python

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  Disclaimer: This presentationis prepared by trainees of baabtra as a part of mentoring program. This is not official document of baabtra –Mentoring Partner Baabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt . Ltd
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  EXCEPTIONS IN PYTHON SHAMEENA.V shameenavayoli@gmail.com www.facebook.com/shamee nalatheef twitter.com/shameena in.linkedin.com/in/shamean 9567135569
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  Introduction : Python usesexceptions to communicate errors and anomalies  exception is an object that indicates an error or anomalous condition code explicitly raise an exception by executing a raise statement.  If a program does not handle an exception, it terminates with an error traceback message
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  The try Statement •The try statement provides Python's exception-handling mechanism • It is a compound statement • It can take one of two different forms: 1) try clause followed by one or more except clauses 2) A try clause followed by exactly one finally clause
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  1)try/except Syntax: try: statement(s) except [expression [,target]]: statement(s) [else: statement(s)]
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  Contd…. • The bodyof each except clause is known as an exception handler
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  2) try/finally Syntax: try: statement(s) finally: statement(s) The finallyclause establishes what is known as a clean-up handler
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  Example : f =open(someFile, "w") try: do_something_with_file(f) finally: f.close( )
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  Built-In Exception classes •BaseException mother of all exceptions • Exception : StandardError(base class for all built in exception) ArithmeticError FloatingPointError OverflowError ZeroDivisionError
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  AttributeError (On attributereference or assignment failure ) EnvironmentError (On error outside Python) IOError OSError WindowsError ImportError (On failure of import to find module or name.) LookupError base class for IndexError, KeyError – IndexError On out-of-range sequence subscript - KeyError On reference to a non-existent mapping (dict) key
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  NameError UnBoundLocalError On reference toan unassigned local variable SyntaxError On parser encountering a syntax error – IndentationError On parser encountering an indentation syntax error --TabError On improper mixture of spaces and tabs
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  Example: try: con = psycopg2.connect(database='testdb',user='shafeequemonp' ) cur = con.cursor() print "Connecting to databasen ->%s" % (con) cur.execute("""INSERT INTO tbl_user(vchr_username) VALUES(%s)""",(ins_login_base.str_name)) con.commit() except psycopg2.DatabaseError, e: if con: con.rollback() print 'Error %s' % e sys.exit(1) finally: if con: con.close() return
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  THANKS
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