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OPERATORS AND OPERANDS Operators
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- Điều hướng trang này:
- floor division
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OPERATORS AND OPERANDS Operators are special symbols that represent computations like addition and multiplication. The values the operator is applied to are called operands. The operators +, -, *, / and ** perform addition, subtraction, multiplication, division and exponentiation, as in the following examples: 20+32 hour-1 hour*60+minute minute/60 5**2 (5+9)*(15-7) In some other languages, ˆ is used for exponentiation, but in Python it is a bitwise operator called XOR. I won’t cover bitwise operators in this book, but you can read about them at wiki.python.org/moin/BitwiseOperators. The division operator might not do what you expect: >>> minute = 59 >>> minute/60 0 The value of minute is 59, and in conventional arithmetic 59 divided by 60 is 0.98333, not 0. The reason for the discrepancy is that Python is performing floor division. † When both of the operands are integers, the result is also an integer; floor division chops off the fraction part, so in this example it rounds down to zero. † In Python 3.0, the result of this division is a float. The new operator // performs integer division. 2.7 Order of Operations 15 If either of the operands is a floating-point number, Python performs floating-point division, and the result is a float: >>> minute/60.0 0.98333333333333328 2.6 EXPRESSIONS An expression is a combination of values, variables, and operators. A value all by itself is considered an expression, and so is a variable, so the following are all legal expressions (assuming that the variable x has been assigned a value): 17 x x + 17 If you type an expression in interactive mode, the interpreter evaluates it and displays the result: >>> 1 + 1 2 But in a script, an expression all by itself doesn’t do anything! This is a common source of confusion for beginners. Exercise 2.2 Type the following statements in the Python interpreter to see what they do: 5 x = 5 x + 1 Now put the same statements into a script and run it. What is the output? Modify the script by transforming each expression into a print statement and then run it again. tải về 1.38 Mb. Chia sẻ với bạn bè của bạn:
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