Python Tutorial

Python Tutorial, Release 2.6.2
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>>> 7/-3
-3
The equal sign (’=’) is used to assign a value to a variable. Afterwards, no result is displayed before the next
interactive prompt:
>>> width = 20
>>> height = 5*9
>>> width * height
900
A value can be assigned to several variables simultaneously:
>>> x = y = z = 0 # Zero x, y and z
>>> x
0
>>> y
0
>>> z
0
Variables must be “defined” (assigned a value) before they can be used, or an error will occur:
>>> # try to access an undefined variable
... n
Traceback (most recent call last):
File "", line 1, in
NameError: name ’n’ is not defined
There is full support for floating point; operators with mixed type operands convert the integer operand to floating
point:
>>> 3 * 3.75 / 1.5
7.5
>>> 7.0 / 2
3.5
Complex numbers are also supported; imaginary numbers are written with a suffix of j or J. Complex numbers
with a nonzero real component are written as (real+imagj), or can be created with the complex(real,
imag) function.
>>> 1j * 1J
(-1+0j)
>>> 1j * complex(0,1)
(-1+0j)
>>> 3+1j*3
(3+3j)
>>> (3+1j)*3
(9+3j)
>>> (1+2j)/(1+1j)
(1.5+0.5j)
Complex numbers are always represented as two floating point numbers, the real and imaginary part. To extract
these parts from a complex number z, use z.real and z.imag.
10 Chapter 3. An Informal Introduction to Python