python内置函数之print

Python内置函数 builtins.print 基本用法。

• builtins.repr
• builtins.print

在 Python 2 中，print 为关键字；在 Python 3 中，print 为内置函数（builtins.print）。

builtins 的 print() 函数：

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

在 Python 3 中可执行 help(print) 查看 print 函数说明：

>>> 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.

Python3 已经不支持 print 的非函数格式了，必须使用 print() 函数调用格式。

>>> print 'hello,world!'
  File "<stdin>", line 1
    print 'hello,world!'
                       ^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print('hello,world!')?

Python print函数用法
python格式化输出
python2与python3的print

---

对很多应用程序来说，使用模块 logging 来写入日志比使用 print 更合适。

相关模块参考：syslog, logging。

sep & end

sep

print 一行打印多个变量（逗号分隔），默认会以空格（sep=' '）分隔：

>>> year=2019
>>> month=10
>>> day=1
>>> print(year,month,day)
2019 10 1

可以指定 sep 参数，定制行内分隔（连接）符：

>>> print(year,month,day,sep='')
2019101
>>> print(year,month,day,sep='-')
2019-10-1

另外一个例子：print 打印日志起始行 tuple，两行之间插了一个空格：

mbr_start_line = '2019-09-22 21:41:59.416 Debug|1031|137920|:96|IMPDT_MBR_Engine||start: role = 1\n'
mbr_stop_line = '2019-09-22 21:43:59.947 Debug|1031|672495|:125|IMPDT_MBR_Engine||stop: reset role from 1\n'
print(mbr_start_line, mbr_stop_line)

2019-09-22 21:41:59.416 Debug|1031|137920|:96|IMPDT_MBR_Engine||start: role = 1
 2019-09-22 21:43:59.947 Debug|1031|672495|:125|IMPDT_MBR_Engine||stop: reset role from 1

可以指定 sep 去掉空格：print(mbr_start_line, mbr_stop_line,sep='')

end

mbr_start_line = '2019-09-22 21:41:59.416 Debug|1031|137920|:96|IMPDT_MBR_Engine||start: role = 1\n'
mbr_stop_line = '2019-09-22 21:43:59.947 Debug|1031|672495|:125|IMPDT_MBR_Engine||stop: reset role from 1\n'
#print(mbr_start_line),print(mbr_stop_line)
mbr_border_lines = (mbr_start_line, mbr_stop_line) # make tuple
for line in mbr_border_lines:
    print(line)

打印结果为：

2019-09-22 21:41:59.416 Debug|1031|137920|:96|IMPDT_MBR_Engine||start: role = 1

2019-09-22 21:43:59.947 Debug|1031|672495|:125|IMPDT_MBR_Engine||stop: reset role from 1

由于按文本读出的行末尾本身就有换行符，因此在连续打印多行日志时，可考虑将 print 在尾部追加的换行符置空，或定制其他行间分隔符。

将 print(line) 修改为 print(line, end='') 即可。

expr

print(var) 或 print(expr) 打印变量或表达式的值。

>>> start=1
>>> stop=10
>>> step=2

>>> print(start)
1

>>> print(start+step)
3

>>> r=range(1,10,2)
# python2
>>> print(r)
[1, 3, 5, 7, 9]
# python3
>>> print(r)
range(1, 10, 2)

>>> l1=[1,2,3,4]
>>> print(l1)
[1, 2, 3, 4]

repr

print(object) 输出类型或描述信息。

#######################################
# 打印模块信息
#######################################
# python3
>>> print(builtins)
<module 'builtins' (built-in)>

>>> print(array)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'array' is not defined
>>> import array

# python2
>>> print(array)
<module 'array' from '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-dynload/array.so'>

# python3
>>> print(array)
<module 'array' from '/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/lib-dynload/array.cpython-36m-darwin.so'>

除此之外，调用 repr(obj) 可以获取该 obj 对象实例的描述信息。

repr 实际上调用的是 obj 的 __repr__ 方法：repr(obj) = obj.__repr__()

>>> help(repr)

Help on built-in function repr in module builtins:

repr(obj, /)
    Return the canonical string representation of the object.

    For many object types, including most builtins, eval(repr(obj)) == obj.

部分示例如下：

#######################################
# 打印模块类型信息
#######################################

>>> print(list)
<class 'list'>

>>> repr(list)
"<class 'list'>"

>>> print(len)
<built-in function len>

>>> repr(len)
'<built-in function len>'

>>> print(hex)
<built-in function hex>

>>> repr(hex)
'<built-in function hex>'

#######################################
# 打印对象实例描述（__repr__）
#######################################

>>> print(sys.version_info)
sys.version_info(major=3, minor=6, micro=5, releaselevel='final', serial=0)

>>> repr(sys.version_info)
"sys.version_info(major=3, minor=9, micro=13, releaselevel='final', serial=0)"

>>> print(sys.thread_info)
sys.thread_info(name='pthread', lock='mutex+cond', version=None)

>>> repr(sys.thread_info)
"sys.thread_info(name='pthread', lock='mutex+cond', version=None)"

list vars

逗号后直接接变量，Python 2 下输出 tuple；Python 3 将自动拼接前半句字面量和后面的变量，以空格（space-separated with sep=' '）隔开。

>>> start=0
>>> stop=30
>>> step=5

# python2 下的输出 tuple
>>> print('start is', start)
('start is', 0)
>>> print('start, stop is', start, stop)
('start, stop is', 0, 30)

# python3 下的输出
>>> print('start is', start)
start is 0
>>> print('start, stop is', start, stop)
start, stop is 0 30

变量也可穿插在中间：

>>> name = "John"
>>> score = 85
>>> print("Total score for", name, "is", score)
Total score for John is 85

format

可参考 builtins.format 和 str.format 函数，输入 help('FORMATTING') 可查看字符串格式化相关议题。

• 参考 builtins.str.format、builtins.string。

printf-style

printf-style String Formatting

C printf 风格，使用 % 格式符标识占位，

# start 可加括号
>>> print('start is %d' % start)
start is 0

>>> print('start,stop is %d, %d' % (start, stop))
start,stop is 0, 30

以下采用 C-printf-style，控制字符串截断输出：

>>> 'i love %s' % 'python'
'i love python'
>>> 'i love %.2s' % 'python'
'i love py'

# 截取两位，总共三位，默认右对齐
>>> 'i love %3.2s' % 'python'
'i love  py'

# 截取两位，总共十位，默认右对齐
>>> 'i love %10.2s' % 'python'
'i love         py'

# 截取两位，总共十位，设置左对齐
>>> 'i love %-10.2s' % 'python'
'i love py        '

# 截取两位，总共十位，设置左对齐
>>> 'i love %-10.2s !' % 'python'
'i love py         !'

format specifier

在占位序号或关键字之后可以 : 来设置填充（fill）、对齐（align）、位宽（width）、进制（base）等格式控制。

An optional ':' and format specifier can follow the field name. This allows greater control over how the value is formatted.

1. 设置打印进制格式(str.format)

>>> # format also supports binary numbers
>>> "int: {0:d};  hex: {0:x};  oct: {0:o};  bin: {0:b}".format(42)
'int: 42;  hex: 2a;  oct: 52;  bin: 101010'

>>> # with 0x, 0o, or 0b as prefix:
>>> "int: {0:d};  hex: {0:#x};  oct: {0:#o};  bin: {0:#b}".format(42)
'int: 42;  hex: 0x2a;  oct: 0o52;  bin: 0b101010'

2. 设置浮点数位数(str.format)

>>> import math
>>> print('The value of PI is approximately {0:.3f}.'.format(math.pi))
The value of PI is approximately 3.142.

>>> '{0:6.2f}'.format(math.pi)
'  3.14'
>>> '{0:>6.2f}'.format(math.pi)
'  3.14'
>>> '{0:<6.2f}'.format(math.pi)
'3.14  '

3. 设置输出宽度及填充格式(str.format)

   Aligning the text and specifying a width

# default align left, fill right with spaces
>>> '{:30}'.format('left aligned')
'left aligned                  '
>>> '{:<30}'.format('left aligned')
'left aligned                  '
>>> '{:>30}'.format('right aligned')
'                 right aligned'
>>> '{:^30}'.format('centered')
'           centered           '
>>> '{:*^30}'.format('centered')  # use '*' as a fill char
'***********centered***********'
>>> '{:-^30}'.format('centered')  # use '-' as a fill char
'-----------centered-----------'

Passing an integer after the ':' will cause that field to be a minimum number of characters wide. This is useful for making tables pretty.

# position:{width}{base}
>>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678}
>>> for name, phone in table.items():
...     print('{0:10} ==> {1:10d}'.format(name, phone))
... 
Sjoerd     ==>       4127
Jack       ==>       4098
Dcab       ==>       7678

4. 逗号千位分隔（Using the comma as a thousands separator）

# 对整数进行千位分隔
>>> str1 = '{:,}'.format(1234567890)
>>> str1
'1,234,567,890'

# 去掉千位分隔符
>>> int(str1.replace(',', ''))
1234567890

5. 输出百分数(str.format)

>>> points = 19
>>> total = 22
>>> 'Correct rate of answers: {:.2%}'.format(points/total)
'Correct rate of answers: 86.36%'

f-string

2. Lexical analysis | 2.4. Literals | 2.4.3. f-strings

Added in version 3.6.
Added in version 3.8: The equal sign '='.

PLS ref to str.format.

color

python - How do I print colored text to the terminal?

Print Colors in Python terminal - GeeksforGeeks

The most common ways to do this are using:

1. Using colorama Module
2. Using termcolor Module
3. Using ANSI Code in Python

Here are several ways to print colored text in Python:

ANSI Escape

ANSI escape codes are special character sequences that control text formatting in terminals.
You can embed these codes directly into your print statements.

RED = '\033[31m'
GREEN = '\033[32m'
RESET = '\033[0m'

print(f"{RED}This text is red.{RESET}")
print(f"{GREEN}This text is green.{RESET}")

Explanation:

• \033[ is the escape sequence initiator.
• 31m sets the text color to red, 32m to green.
• 0m resets the color to default.

python打印各种文本颜色
python中print打印显示颜色
Python基础之控制台输出颜色
python用print输出不同颜色字体

显示颜色的格式：\033[显示方式;字体色;背景色m ...... \033[0m

显示方式	效果	字体色	背景色	颜色描述
0	终端默认设置	30	40	黑色
1	高亮显示	31	41	红色
4	使用下划线	32	42	绿色
5	闪烁	33	43	黄色
7	反白显示	34	44	蓝色
8	不可见	35	45	紫红色
N/A	N/A	36	46	青蓝色
N/A	N/A	37	47	白色

print("\033[4;34m下划线，蓝色字体\033[0m")
print("\033[1;4;34m加粗(高亮)，下划线，蓝色字体\033[0m")
print("\033[1;4;34;42m加粗(高亮)，下划线，蓝色字体，绿色背景\033[0m")

termcolor

The termcolor library provides a more convenient way to color text.

from termcolor import colored

print(colored('Hello, World!', 'red'))
print(colored('Hello, World!', 'green', attrs=['bold']))

Explanation:

• colored() function takes the text and color as arguments.
• You can also add attributes like bold, underline, etc.

colorama

colorama is a cross-platform library that makes ANSI escape codes work on Windows as well.

The colors that Fore & Back support:

• BLACK/LIGHTBLACK_EX
• RED/LIGHTRED_EX
• GREEN/LIGHTGREEN_EX
• YELLOW/LIGHTYELLOW_EX
• BLUE/LIGHTBLUE_EX
• MAGENTA/LIGHTMAGENTA_EX: 紫红色（品红色）
• CYAN/LIGHTCYAN_EX: 青蓝色（蓝绿色）
• WHITE/LIGHTWHITE_EX

Style provides the following attributes:

• NORMAL
• DIM: 昏暗，暗淡
• BRIGHT：高亮，加粗

Style.RESET_ALL resets foreground, background, and brightness. Colorama will perform this reset automatically on program exit.

import colorama
from colorama import Fore, Back, Style

print(Fore.RED + 'some red text')
print(Back.GREEN + 'and with a green background')
print(Style.DIM + 'and in dim text')
print(Style.RESET_ALL)
print('back to normal now')

If you find yourself repeatedly sending reset sequences to turn off color changes at the end of every print, then init(autoreset=True) will automate that for you.

import colorama
from colorama import Fore, Back, Style

colorama.init(autoreset=True)

print(Fore.RED + "This text is red.")
print(Fore.GREEN + "This text is green.")
print(Back.YELLOW + "Background is yellow.")
print(Style.BRIGHT + "This text is bright.")

Explanation:

• colorama.init() initializes colorama.
• Fore, Back, Style provide color and style options.

import colorama
from colorama import Fore, Back, Style

colorama.init(autoreset=True)

def test_fore():
    print(Fore.WHITE + 'Fore.WHITE')
    print(Fore.BLACK + 'Fore.BLACK')
    print(Fore.RED + 'Fore.RED')
    print(Fore.GREEN + 'Fore.GREEN')
    print(Fore.YELLOW + 'Fore.YELLOW')
    print(Fore.BLUE + 'Fore.BLUE')
    print(Fore.MAGENTA + 'Fore.MAGENTA')
    print(Fore.CYAN + 'Fore.CYAN')

def test_fore_light():
    print(Fore.LIGHTWHITE_EX + 'Fore.LIGHTWHITE_EX')
    print(Fore.LIGHTBLACK_EX + 'Fore.LIGHTBLACK_EX')
    print(Fore.LIGHTRED_EX + 'Fore.LIGHTRED_EX')
    print(Fore.LIGHTGREEN_EX + 'Fore.LIGHTGREEN_EX')
    print(Fore.LIGHTYELLOW_EX + 'Fore.LIGHTYELLOW_EX')
    print(Fore.LIGHTBLUE_EX + 'Fore.LIGHTBLUE_EX')
    print(Fore.LIGHTMAGENTA_EX + 'Fore.LIGHTMAGENTA_EX')
    print(Fore.LIGHTCYAN_EX + 'Fore.LIGHTCYAN_EX')

def test_fore_back():
    print(Fore.BLACK + Back.LIGHTWHITE_EX + 'Fore.BLACK, Back.LIGHTWHITE_EX')
    print(Fore.RED + Back.LIGHTWHITE_EX + 'Fore.RED, Back.LIGHTWHITE_EX')
    print(Fore.GREEN + Back.LIGHTWHITE_EX + 'Fore.GREEN, Back.LIGHTWHITE_EX')
    print(Fore.YELLOW + Back.LIGHTWHITE_EX + 'Fore.YELLOW, Back.LIGHTWHITE_EX')
    print(Fore.BLUE + Back.LIGHTWHITE_EX + 'Fore.BLUE, Back.LIGHTWHITE_EX')
    print(Fore.MAGENTA + Back.LIGHTWHITE_EX + 'Fore.MAGENTA, Back.LIGHTWHITE_EX')
    print(Fore.CYAN + Back.LIGHTWHITE_EX + 'Fore.CYAN, Back.LIGHTWHITE_EX')

def prompt_missing_password():
    print("No password found in os.environ, PLS export", end=' ')
    print(f"{Style.BRIGHT}{Back.LIGHTYELLOW_EX}EXCEL_PASSWD", end=' ')
    print("before running this program!")

if __name__ == '__main__':
    prompt_missing_password()
else:
    pass

rich

Textualize/rich / README.md - documentation

print with markup

• Console Markup
• Pretty Printing

To effortlessly add rich output to your application, you can import the rich print method, which has the same signature as the builtin Python function. Try this:

from rich import print

print("Hello, [bold magenta]World[/bold magenta]!", ":vampire:", locals())

Console.print with style

documentation - rich.console

For more control over rich terminal content, import and construct a Console object.

The Console object has a print method which has an intentionally similar interface to the builtin print function.

• Console.print: Print to the console.

from rich.console import Console

console = Console()

The Console object has a print method which has an intentionally similar interface to the builtin print function. Here's an example of use:

console.print("Hello", "World!")

As you might expect, this will print "Hello World!" to the terminal. Note that unlike the builtin print function, Rich will word-wrap your text to fit within the terminal width.

There are a few ways of adding color and style to your output. You can set a style for the entire output by adding a style keyword argument, see Styles. Here's an example:

console.print("Hello", "World!", style="bold red")

That's fine for styling a line of text at a time. For more finely grained styling, Rich renders a special markup which is similar in syntax to bbcode. Here's an example:

console.print("Where there is a [bold cyan]Will[/bold cyan] there [u]is[/u] a [i]way[/i].")

The Console object has a log() method which has a similar interface to print(), but also renders a column for the current time and the file and line which made the call. By default Rich will do syntax highlighting for Python structures and for repr strings. If you log a collection (i.e. a dict or a list) Rich will pretty print it so that it fits in the available space.

• Console.log: Log rich content to the terminal.

alternative markup to colorama

Colorama Attribute	Rich Markup Example	Rich Style Object Example	Description
Fore.RED Fore.LIGHTRED_EX	[red]Text[/red] [bright_red]Text[/bright_red]	Style(color="red") Style(color="bright_red")	Sets the foreground color.
Back.CYAN Back.LIGHTCYAN_EX	[on cyan]Text[/on cyan] [on bright_cyan]Text[/on bright_cyan]	Style(bgcolor="cyan")	Sets the background color.
Style.BRIGHT	[bold]Text[/bold]	Style(bold=True)	Makes text bold/bright.
Style.NORMAL	[not bold]Text[/not bold] (to disable)	Style(bold=False)	Resets brightness/bolding.
Style.RESET_ALL	[not bold not italic on default]Text[/not bold not italic on default] (disable specific styles)	Use console.print() without a style, or define a new Style that is the base style	Resets all formatting to default.

Use rich.print instead of print+colorama to output colored message:

import rich

def test_fore_back():
    # print(Fore.BLACK + Back.LIGHTWHITE_EX + 'Fore.BLACK, Back.LIGHTWHITE_EX')
    rich.print('[black on bright_white]Fore.BLACK, Back.LIGHTWHITE_EX[/black on bright_white]')
    # print(Fore.RED + Back.LIGHTWHITE_EX + 'Fore.RED, Back.LIGHTWHITE_EX')
    rich.print('[red on bright_white]Fore.RED, Back.LIGHTWHITE_EX[/red on bright_white]')
    # print(Fore.GREEN + Back.LIGHTWHITE_EX + 'Fore.GREEN, Back.LIGHTWHITE_EX')
    rich.print('[green on bright_white]Fore.GREEN, Back.LIGHTWHITE_EX[/green on bright_white]')
    # print(Fore.YELLOW + Back.LIGHTWHITE_EX + 'Fore.YELLOW, Back.LIGHTWHITE_EX')
    rich.print('[yellow on bright_white]Fore.YELLOW, Back.LIGHTWHITE_EX[/yellow on bright_white]')
    # print(Fore.BLUE + Back.LIGHTWHITE_EX + 'Fore.BLUE, Back.LIGHTWHITE_EX')
    rich.print('[blue on bright_white]Fore.BLUE, Back.LIGHTWHITE_EX[/blue on bright_white]')
    # print(Fore.MAGENTA + Back.LIGHTWHITE_EX + 'Fore.MAGENTA, Back.LIGHTWHITE_EX')
    rich.print('[magenta on bright_white]Fore.MAGENTA, Back.LIGHTWHITE_EX[/magenta on bright_white]')
    # print(Fore.CYAN + Back.LIGHTWHITE_EX + 'Fore.CYAN, Back.LIGHTWHITE_EX')
    rich.print('[cyan on bright_white]Fore.CYAN, Back.LIGHTWHITE_EX[/cyan on bright_white]')

def prompt_missing_password():
    print("No password found in os.environ, PLS export", end=' ')
    # print(f"{Style.BRIGHT}{Back.LIGHTYELLOW_EX}EXCEL_PASSWD", end=' ')
    rich.print("[bold on bright_yellow]EXCEL_PASSWD[/bold on bright_yellow]", end=' ')
    print("before running this program!")

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