Introduction to Python Basics

Introduction to Python Basics

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  Python – Basics byRaghunath Akula
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  Python Overview  Pythonis a great and friendly language to use & learn, can be adapted to small & big projects.  Open source general-purpose language and with great supports for Oops.  Python is formally an Interpreted language.  Fast array operations – 2D / multi-D arrays, linear algebra etc.  Easy to interface with Java / C / ObjC  Offers Matlab-ish capabilities within Python.
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  Integer  num= 8 Float  num = 3.456 String  “abc” or ‘abc’ Triple double-quotes for multi-line strings ””” this is veryyy long string…””” Basic Datatypes Whitespace  Whitespace is used to denote blocks. In other languages curly brackets { … } are common.  When you indent, it becomes a child of the previous line.  The parent can also has a colon(:) following it. >>> Parent: child_1: grand_child_1 child_2: grand_child_2
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  Comments  Start commentswith # – the rest of line is ignored.  Can include a “documentation string” as the first line of any new function or class that you define.  Multiline comments – ”””… ”””. Similar to /* */ in java. Naming Rules  Names are case sensitive and cannot start with a number. They can contain letters, numbers, and underscores. rax Rax _rax _2_rax_ rax_2 RaX  There are some reserved words: and, assert, break, class, continue, def, del, elif, else, except, exec, finally, for, from, global, if, import, in, is, lambda, not, or, pass, print, raise, return, try, while
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   Binding avariable in Python means setting a name to hold a reference to some object.  Python determines the type of the reference automatically based on the data object assigned to it.  Name is created for the first time it appears on the left side of an assignment expression >>> X = 3  A reference is deleted via garbage collection after any names bound to it have passed out of scope. >>> fname, lname = ‘Raghu’, ‘Akula’ >>> fname ‘Raghu’ >>> lname ‘Akula’ Identifiers
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   Logical Operator notunary negation and conditional_and or conditional_or  Equality Operator is same identity is not different identity == equivalent != not equivalent  Comparison Operator < less than < = less than or equal to > greater than > = greater than or equal to  Arithmetic Operator + addition − subtraction * multiplication / true division // integer division % modulo operator Operators And Expressions  Bitwise Operator ∼ bitwise complement (prefix unary operator) & bitwise and | bitwise or ˆ bitwise exclusive-or << shift bits left, filling in with zeros >> shift bits right, filling in with sign bit  Sequence Operator s[j] element at index j s[start:stop] slice including indices [start,stop) s + t concatenation of sequences k * s shorthand for s + s +... (k times) val in s containment check val not in s non-containment check
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  Control Flow  Conditional ifa > 10: print (“a is greater than 10.”) eif a < 10: print (“a is lesser than 10.”) else print (“a is equals to 10.”)  While Loop n = 20 s = 0 count = 1 while counter <= n: s = s + count count += 1 print (“Sum = ”, count)  For Loop # Squares of numbers [1,4,9,16,…] squares = [] for k in range(1, n+1): squares.append(k*k) # with List comprehension squares = [k*k for k in range(1, n+1)]  Break & Continue x = 3 While x < 10 : if x > 7 : x = x + 2 continue x = x + 1 print “Inside loop.” if x == 8: break
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   Python isa dynamically typed language, types are dynamically designated to parameter(s).  Each time a function is called, Python creates a dedicated activation record that stores information relevant to the current call.  “def” creates a function and assigns it a name >>> def function_name(arg1, arg2, ..., argN): <statements> return >>> def compute_gradeAverage(grades): points{‘A’:5, ‘B’:4, ‘C’:3, ‘D’:2, ‘E’:1} num_courses = 0 total_points = 0 for g in grades: num_courses += 1 total_points += points[g] return total_points / num_courses Functions
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   Identifiers usedto describe the expected parameters are known as formal parameters, and the objects sent by the caller when invoking the function are the actual parameters.  A caller can invoke a function with varying number of actual parameters  Changing a mutable argument may affect the caller >>> def sum(arg_1,arg_2): total = arg_1 + arg_2 return total  Can define defaults for arguments that need not be passed >>> def func(a, b, c=10, d=100): print a, b, c, d >>> func(1,2) 1 2 10 100 >>> func(1,2,3,4) 1,2,3,4 Functions – Passing Arguments
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  Exception Handling  Exceptionsare unexpected events that occur during the execution of a program.  An exception might result from a logical error or an unanticipated situation.  A raised error may be caught by a surrounding context that handles the exception in an appropriate fashion.  If uncaught, an exception causes the interpreter to stop executing  The try-except clause is best used when there is reason to believe that the exceptional case is relatively unlikely  Particularly useful when working with user input or when reading / writing to files >>> try: <statements> except: print(“error statement”) finally: print(“gets executed no matter what”)
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  Thank you!!