两天研习Python基础（三） 函数

#!/usr/bin/python3

# ----- function without arguments -----
def greeting():
    print("-----------------------------")
    print("         Hello World         ")
    print("-----------------------------")

greeting()

# ----- 带参数的函数 -----
def sum_two_numbers(num1, num2):
    total = num1 + num2
    print("{} + {} = {}".format(num1, num2, total))

sum_two_numbers(3, 4)

# ----- 带返回值的函数 -----
def num_square(num):
    return num * num

my_num = 3
print(num_square(2))
print(num_square(my_num))

$ ./functions.py
-----------------------------
         Hello World
-----------------------------
3 + 4 = 7
4
9

#!/usr/bin/python3

# ----- function with default valued argument -----
def greeting(style_char='-'):
    print(style_char * 29)
    print("         Hello World         ")
    print(style_char * 29)

print("Default style")
greeting()

print("\nStyle character *")
greeting('*')

print("\nStyle character =")
greeting(style_char='=')

$ ./functions_default_arg_value.py
Default style
-----------------------------
         Hello World
-----------------------------

Style character *
*****************************
         Hello World
*****************************

Style character =
=============================
         Hello World
=============================

def num_square(num):
    """
    returns square of number
    """

    return num * num

>>> print("hi")
hi
>>> print("hi", end='')
hi>>>
>>> print("hi", end=' !!\n')
hi !!
>>>

>>> help(print)

Help on built-in function print in module builtins:

print(...)
    print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)

    Prints the values to a stream, or to sys.stdout by default.
    Optional keyword arguments:
    file:  a file-like object (stream); defaults to the current sys.stdout.
    sep:   string inserted between values, default a space.
    end:   string appended after the last value, default a newline.
    flush: whether to forcibly flush the stream.

>>> a = 5
>>> b = 2

>>> print(a+b, a-b)
7 3

>>> print(a+b, a-b, sep=' : ')
7 : 3

>>> print(a+b, a-b, sep='\n')
7
3

>>> greeting = 'Hello World'
>>> print(greeting)
Hello World
>>> num = 42
>>> print(num)
42

>>> print(greeting + '. We are learning Python')
Hello World. We are learning Python
>>> print(greeting, '. We are learning Python', sep='')
Hello World. We are learning Python

>>> print("She bought " + num + " apples")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Can't convert 'int' object to str implicitly

>>> print("She bought " + str(num) + " apples")
She bought 42 apples

>>> print("She bought", num, "apples")
She bought 42 apples

>>> items = 15
>>> print("No. of items:", items)
No. of items: 15

>>> print("No. of items:", items, sep='')
No. of items:15

>>> import sys
>>> print("Error!! Not a valid input", file=sys.stderr)
Error!! Not a valid input

>>> num1 = 42
>>> num2 = 7

>>> '{} + {} = {}'.format(num1, num2, num1 + num2)
'42 + 7 = 49'

# 或者将格式保存为一个变量然后在需要的地方使用
>>> op_fmt = '{} + {} = {}'
>>> op_fmt.format(num1, num2, num1 + num2)
'42 + 7 = 49'
>>> op_fmt.format(num1, 29, num1 + 29)
'42 + 29 = 71'

# 在print函数内部使用也当然没问题
>>> print('{} + {} = {}'.format(num1, num2, num1 + num2))
42 + 7 = 49

>>> num1
42
>>> num2
7
>>> print("{0} + {1} * {0} = {2}".format(num1, num2, num1 + num2 * num1))
42 + 7 * 42 = 336

>>> appx_pi = 22 / 7
>>> appx_pi
3.142857142857143

# 在小数点后限制数字的位数
# 数值会进行取舍
>>> print("{0:.2f}".format(appx_pi))
3.14
>>> print("{0:.3f}".format(appx_pi))
3.143

# 对齐
>>> print("{0:<10.3f} and 5.12".format(appx_pi))
3.143      and 5.12
>>> print("{0:>10.3f} and 5.12".format(appx_pi))
     3.143 and 5.12

# 用0填充
>>> print("{0:08.3f}".format(appx_pi))
0003.143

>>> print("42 in binary = {:b}".format(42))
42 in binary = 101010
>>> print("42 in octal = {:o}".format(42))
42 in octal = 52
>>> print("241 in hex = {:x}".format(241))
241 in hex = f1

# 通过#添加0b/0o/0x前缀
>>> print("42 in binary = {:#b}".format(42))
42 in binary = 0b101010

>>> hex_str = "{:x}".format(42)
>>> hex_str
'2a'

# 也可以使用内置的format函数
>>> format(42, 'x')
'2a'
>>> format(42, '#x')
'0x2a'

# 将字符串转换为整型
>>> int(hex_str, base=16)
42
>>> int('0x2a', base=16)
42

>>> num1 = 42
>>> num2 = 7
>>> f'{num1} + {num2} = {num1 + num2}'
'42 + 7 = 49'
>>> print(f'{num1} + {num2} = {num1 + num2}')
42 + 7 = 49

>>> appx_pi = 22 / 7
>>> f'{appx_pi:08.3f}'
'0003.143'

>>> f'{20:x}'
'14'
>>> f'{20:#x}'
'0x14'

>>> range(5)
range(0, 5)

>>> list(range(5))
[0, 1, 2, 3, 4]

>>> list(range(-2, 2))
[-2, -1, 0, 1]

>>> list(range(1, 15, 2))
[1, 3, 5, 7, 9, 11, 13]

>>> list(range(10, -5, -2))
[10, 8, 6, 4, 2, 0, -2, -4]

>>> type(5)
<class 'int'>

>>> type('Hi there!')
<class 'str'>

>>> type(range(7))
<class 'range'>

>>> type(None)
<class 'NoneType'>

>>> type(True)
<class 'bool'>

>>> arr = list(range(4))
>>> arr
[0, 1, 2, 3]
>>> type(arr)
<class 'list'>

#!/usr/bin/python3

def print_num():
    print("Yeehaw! num is visible in this scope, its value is: " + str(num))

num = 25
print_num()

$ ./variable_scope_1.py
Yeehaw! num is visible in this scope, its value is: 25

#!/usr/bin/python3

def square_of_num(num):
    sqr_num = num * num

square_of_num(5)
print("5 * 5 = {}".format(sqr_num))

$ ./variable_scope_2.py
Traceback (most recent call last):
  File "./variable_scope_2.py", line 7, in <module>
    print("5 * 5 = {}".format(sqr_num))
NameError: name 'sqr_num' is not defined

#!/usr/bin/python3

def square_of_num(num):
    global sqr_num
    sqr_num = num * num

square_of_num(5)
print("5 * 5 = {}".format(sqr_num))

$ ./variable_scope_3.py
5 * 5 = 25

#!/usr/bin/python3

sqr_num = 4

def square_of_num(num):
    sqr_num = num * num
    print("5 * 5 = {}".format(sqr_num))

square_of_num(5)
print("Whoops! sqr_num is still {}!".format(sqr_num))

$ ./variable_scope_4.py
5 * 5 = 25
Whoops! sqr_num is still 4!