Python十分钟入门

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>>> help(5)

Help on int object:

(etc etc)

>>> dir(5)

[‘__abs__‘, ‘__add__‘, ...]

>>> abs.__doc__

‘abs(number) -> number

Return the absolute value of the argument.‘

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>>> myvar = 3

>>> myvar += 2

>>> myvar

5

>>> myvar -= 1

>>> myvar

4

"""This is a multiline comment.

The following lines concatenate the two strings."""

>>> mystring = "Hello"

>>> mystring += " world."

>>> print mystring

Hello world.

# This swaps the variables in one line(!).

# It doesn‘t violate strong typing because values aren‘t

# actually being assigned, but new objects are bound to

# the old names.

>>> myvar, mystring = mystring, myvar

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>>> sample = [1, ["another", "list"], ("a", "tuple")]

>>> mylist = ["List item 1", 2, 3.14]

>>> mylist[0] = "List item 1 again" # We‘re changing the item.

>>> mylist[-1] = 3.21 # Here, we refer to the last item.

>>> mydict = {"Key 1": "Value 1", 2: 3, "pi": 3.14}

>>> mydict["pi"] = 3.15 # This is how you change dictionary values.

>>> mytuple = (1, 2, 3)

>>> myfunction = len

>>> print myfunction(mylist)

3

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>>> mylist = ["List item 1", 2, 3.14]

>>> print mylist[:]

[‘List item 1‘, 2, 3.1400000000000001]

>>> print mylist[0:2]

[‘List item 1‘, 2]

>>> print mylist[-3:-1]

[‘List item 1‘, 2]

>>> print mylist[1:]

[2, 3.14]

# Adding a third parameter, "step" will have Python step in

# N item increments, rather than 1.

# E.g., this will return the first item, then go to the third and

# return that (so, items 0 and 2 in 0-indexing).

>>> print mylist[::2]

[‘List item 1‘, 3.14]

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>>>print "Name: %s\

Number: %s\

String: %s" % (myclass.name, 3, 3 * "-")

Name: Poromenos

Number: 3

String: ---

strString = """This is

a multiline

string."""

# WARNING: Watch out for the trailing s in "%(key)s".

>>> print "This %(verb)s a %(noun)s." % {"noun": "test", "verb": "is"}

This is a test.

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rangelist = range(10)

>>> print rangelist

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

for number in rangelist:

    # Check if number is one of

    # the numbers in the tuple.

    if number in (3, 4, 7, 9):

        # "Break" terminates a for without

        # executing the "else" clause.

        break

    else:

        # "Continue" starts the next iteration

        # of the loop. It‘s rather useless here,

        # as it‘s the last statement of the loop.

        continue

else:

    # The "else" clause is optional and is

    # executed only if the loop didn‘t "break".

    pass # Do nothing

if rangelist[1] == 2:

    print "The second item (lists are 0-based) is 2"

elif rangelist[1] == 3:

    print "The second item (lists are 0-based) is 3"

else:

    print "Dunno"

while rangelist[1] == 1:

    pass

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# 作用等同于 def funcvar(x): return x + 1

funcvar = lambda x: x + 1

>>> print funcvar(1)

2

# an_int 和 a_string 是可选参数，它们有默认值

# 如果调用 passing_example 时只指定一个参数，那么 an_int 缺省为 2 ，a_string 缺省为 A default string。如果调用 passing_example 时指定了前面两个参数，a_string 仍缺省为 A default string。

# a_list 是必备参数，因为它没有指定缺省值。

def passing_example(a_list, an_int=2, a_string="A default string"):

    a_list.append("A new item")

    an_int = 4

    return a_list, an_int, a_string

>>> my_list = [1, 2, 3]

>>> my_int = 10

>>> print passing_example(my_list, my_int)

([1, 2, 3, ‘A new item‘], 4, "A default string")

>>> my_list

[1, 2, 3, ‘A new item‘]

>>> my_int

10

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class MyClass(object):

    common = 10

    def __init__(self):

        self.myvariable = 3

    def myfunction(self, arg1, arg2):

        return self.myvariable

    # This is the class instantiation

>>> classinstance = MyClass()

>>> classinstance.myfunction(1, 2)

3

# This variable is shared by all classes.

>>> classinstance2 = MyClass()

>>> classinstance.common

10

>>> classinstance2.common

10

# Note how we use the class name

# instead of the instance.

>>> MyClass.common = 30

>>> classinstance.common

30

>>> classinstance2.common

30

# This will not update the variable on the class,

# instead it will bind a new object to the old

# variable name.

>>> classinstance.common = 10

>>> classinstance.common

10

>>> classinstance2.common

30

>>> MyClass.common = 50

# This has not changed, because "common" is

# now an instance variable.

>>> classinstance.common

10

>>> classinstance2.common

50

# This class inherits from MyClass. The example

# class above inherits from "object", which makes

# it what‘s called a "new-style class".

# Multiple inheritance is declared as:

# class OtherClass(MyClass1, MyClass2, MyClassN)

class OtherClass(MyClass):

    # The "self" argument is passed automatically

    # and refers to the class instance, so you can set

    # instance variables as above, but from inside the class.

    def __init__(self, arg1):

        self.myvariable = 3

        print arg1

>>> classinstance = OtherClass("hello")

hello

>>> classinstance.myfunction(1, 2)

3

# This class doesn‘t have a .test member, but

# we can add one to the instance anyway. Note

# that this will only be a member of classinstance.

>>> classinstance.test = 10

>>> classinstance.test

10

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def some_function():

    try:

        # Division by zero raises an exception

        10 / 0

    except ZeroDivisionError:

        print "Oops, invalid."

    else:

        # Exception didn‘t occur, we‘re good.

        pass

    finally:

        # This is executed after the code block is run

        # and all exceptions have been handled, even

        # if a new exception is raised while handling.

        print "We‘re done with that."

>>> some_function()

Oops, invalid.

We‘re done with that.

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import random

from time import clock

randomint = random.randint(1, 100)

>>> print randomint

64

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import pickle

mylist = ["This", "is", 4, 13327]

# Open the file C:\\binary.dat for writing. The letter r before the

# filename string is used to prevent backslash escaping.

myfile = open(r"C:\\binary.dat", "w")

pickle.dump(mylist, myfile)

myfile.close()

myfile = open(r"C:\\text.txt", "w")

myfile.write("This is a sample string")

myfile.close()

myfile = open(r"C:\\text.txt")

>>> print myfile.read()

‘This is a sample string‘

myfile.close()

# Open the file for reading.

myfile = open(r"C:\\binary.dat")

loadedlist = pickle.load(myfile)

myfile.close()

>>> print loadedlist

[‘This‘, ‘is‘, 4, 13327]

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>>> lst1 = [1, 2, 3]

>>> lst2 = [3, 4, 5]

>>> print [x * y for x in lst1 for y in lst2]

[3, 4, 5, 6, 8, 10, 9, 12, 15]

>>> print [x for x in lst1 if 4 > x > 1]

[2, 3]

# Check if an item has a specific property.

# "any" returns true if any item in the list is true.

>>> any([i % 3 for i in [3, 3, 4, 4, 3]])

True

# This is because 4 % 3 = 1, and 1 is true, so any()

# returns True.

# Check how many items have this property.

>>> sum(1 for i in [3, 3, 4, 4, 3] if i == 4)

2

>>> del lst1[0]

>>> print lst1

[2, 3]

>>> del lst1