python learn 01 basic

摘要：输入的模块上使用。我们看到它包含一个庞大的属性列表。默认地，它返回当前模块的属性列表。

Python Learn Part

More_Info

Content List

1.Python Introduce

1.1 python REPL

1.2 python helloworld.py

1.3 python help()

1.4 to python_string

1.5 difference between input and raw_input

2.Python Preliminary program

2.1 Operators and Expression

2.2 python control flow

3.function

3.1 local var

3.2 global var

3.3 func_key

3.4 DocStrings

4.Module

4.1 sys module

4.2 from..import

4.3 name

4.4 dir()

python 少有的一种可以称得上即简单又功能强大的编程语言

python 代表简单主义思想的语言

➜  python git:(master) python -V
Python 2.7.10
➜  python git:(master)

➜  python git:(master) python
Python 2.7.10 (default, Jul 14 2015, 19:46:27)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.39)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 2**3 or pow(2, 3)
8
>>> x = input("x:")
x:5
>>> print "hello ", x
hello  5
>>> print 3
3
>>> print "3"
3
>>> 0xAF
175
>>> 010
8
>>> round(1.0/3.0) #四舍五入
0.0
>>> round(1.0/2.0)
1.0
>>> import math
>>> math.floor(32.9)
32.0
>>> print r"C:
owhere"""    # 解决最后一个字符是 "" 的情况！ 完美解决  
C:
owhere  
>>> print u"hello, world"      # Unicode 字符串， 在python3.0中，所有的字符串都是 Unicode 字符串  
hello, world  
>>>

#!/usr/bin/python
# Filename : helloworld.py
print "Hello World"

>>> help()

Welcome to Python 2.7!  This is the online help utility.

help> input
Help on built-in function input in module __builtin__:

input(...)
    input([prompt]) -> value

        Equivalent to eval(raw_input(prompt)).
        (END)

str

repr

backquote

>>> ""hello world" she said"  
""hello world" she said"  
>>> "hello world"  
"hello world"  
>>> 10000L  
10000L  
>>> print "hello world"  
hello world  
>>> print 10000L  
10000  
>>> print str("Hello world")  
Hello world  
>>> print str(10000L)  
10000  

>>> raw_input("shuru : ")  
shuru : 6  
"6"  
>>> input("shuru : ")  #默认为合法的python表达式  
shuru : 5  
5   

>>> i = 5
>>> i = i + 1
>>> print 
... i
6
>>> print i
6
>>>

operator precedence

Expression

#!/usr/bin/python
# Filename: expression.py

length = 5
breadth = 2
area = length * breadth
print "Area is", area
print "Perimeter is", 2 * (length + breadth)

#!/usr/bin/python
# Filename: while.py

number = 23
running = True

while running:
  guess = int(raw_input("Enter an integer : "))

  if guess == number:
    print "Congratulations, you guessed it." 
    running = False # this causes the while loop to stop
  elif guess < number:
    print "No, it is a little higher than that" 
  else:
    print "No, it is a little lower than that" 
else:
  print "The while loop is over." 
  # Do anything else you want to do here

print "Done"

break, continue

#!/usr/bin/python
# Filename: continue.py

while True:
  s = raw_input("Enter something : ")
  if s == "quit":
    break
  if len(s) < 3:
    continue
  print "Input is of sufficient length"
  # Do other kinds of processing here...

#!/usr/bin/python
# Filename: func_local.py

def func(x):
    print "x is", x
    x = 2
    print "Changed local x to", x

x = 50
func(x)
print "x is still", x

Output

$ python func_local.py
x is 50
Changed local x to 2
x is still 50

#!/usr/bin/python
# Filename: func_global.py

def func():
  global x

  print "x is", x
  x = 2
  print "Changed local x to", x

x = 50
func()
print "Value of x is", x

Output

$ python func_global.py
x is 50
Changed global x to 2
Value of x is 2

#!/usr/bin/python
# Filename: func_key.py

def func(a, b=5, c=10):
  print "a is", a, "and b is", b, "and c is", c

  func(3, 7)
  func(25, c=24)
  func(c=50, a=100)

Output

$ python func_key.py
a is 3 and b is 7 and c is 10
a is 25 and b is 5 and c is 24
a is 100 and b is 5 and c is 50

# #!/usr/bin/python
# Filename: func_doc.py

def printMax(x, y):
  """Prints the maximum of two numbers.

    The two values must be integers."""
  x = int(x) # convert to integers, if possible
  y = int(y)

  if x > y:
    print x, "is maximum"
  else:
    print y, "is maximum"
    return y

printMax(3, 5)
print printMax.__doc__

output

$ python func_doc.py
5 is maximum
Prints the maximum of two numbers.

    The two values must be integers.

#!/usr/bin/python
# Filename: using_sys.py

import sys

print "The command line arguments are:"
for i in sys.argv:
  print i

print "

The PYTHONPATH is", sys.path, "
"

yourself module

#!/usr/bin/python
# Filename: mymodule.py

def sayhi():
    print "Hi, this is mymodule speaking."

version = "0.1"

# End of mymodule.py

mymodule_demo.py

#!/usr/bin/python
# Filename: mymodule_demo.py

import mymodule

mymodule.sayhi()
print "Version", mymodule.version

from..import..

#!/usr/bin/python
# Filename: mymodule_demo2.py

from mymodule import sayhi, version
# Alternative:
# from mymodule import *

sayhi()
print "Version", version

#!/usr/bin/python
# Filename: using_name.py

if __name__ == "__main__":
    print "This program is being run by itself"
else:
    print "I am being imported from another module"

每个Python模块都有它的__name__，如果它是"__main__"，这说明这个模块被用户多带带运行，我们可以进行相应的恰当操作。

$ python
>>> import sys
>>> dir(sys) # get list of attributes for sys module
["__displayhook__", "__doc__", "__excepthook__", "__name__", "__stderr__",
"__stdin__", "__stdout__", "_getframe", "api_version", "argv",
"builtin_module_names", "byteorder", "call_tracing", "callstats",
"copyright", "displayhook", "exc_clear", "exc_info", "exc_type",
"excepthook", "exec_prefix", "executable", "exit", "getcheckinterval",
"getdefaultencoding", "getdlopenflags", "getfilesystemencoding",
"getrecursionlimit", "getrefcount", "hexversion", "maxint", "maxunicode",
"meta_path","modules", "path", "path_hooks", "path_importer_cache",
"platform", "prefix", "ps1", "ps2", "setcheckinterval", "setdlopenflags",
"setprofile", "setrecursionlimit", "settrace", "stderr", "stdin", "stdout",
"version", "version_info", "warnoptions"]
>>> dir() # get list of attributes for current module
["__builtins__", "__doc__", "__name__", "sys"]
>>>
>>> a = 5 # create a new variable "a"
>>> dir()
["__builtins__", "__doc__", "__name__", "a", "sys"]
>>>
>>> del a # delete/remove a name
>>>
>>> dir()
["__builtins__", "__doc__", "__name__", "sys"]
>>>

输入的sys模块上使用dir。我们看到它包含一个庞大的属性列表。
dir() , 默认地，它返回当前模块的属性列表。