Python 实用宝典

Question 1

How do I repeat the last command? The usual keys: Up, Ctrl+Up, Alt-p don’t work. They produce nonsensical characters.

(ve)[kakarukeys@localhost ve]$ python
Python 2.6.6 (r266:84292, Nov 15 2010, 21:48:32) 
[GCC 4.4.4 20100630 (Red Hat 4.4.4-10)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> print "hello world"
hello world
>>> ^[[A
  File "<stdin>", line 1
    ^
SyntaxError: invalid syntax
>>> ^[[1;5A
  File "<stdin>", line 1
    [1;5A
    ^
SyntaxError: invalid syntax
>>> ^[p
  File "<stdin>", line 1
    p
    ^
SyntaxError: invalid syntax
>>>

Question 2

I use the following to enable history on python shell.

This is my .pythonstartup file . PYTHONSTARTUP environment variable is set to this file path.

# python startup file 
import readline 
import rlcompleter 
import atexit 
import os 
# tab completion 
readline.parse_and_bind('tab: complete') 
# history file 
histfile = os.path.join(os.environ['HOME'], '.pythonhistory') 
try: 
    readline.read_history_file(histfile) 
except IOError: 
    pass 
atexit.register(readline.write_history_file, histfile) 
del os, histfile, readline, rlcompleter

You will need to have the modules readline, rlcompleter to enable this.

Check out the info on this at : http://docs.python.org/using/cmdline.html#envvar-PYTHONSTARTUP.

Modules required:

Question 3

In IDLE, go to Options -> Configure IDLE -> Keys and there select history-next and then history-previous to change the keys.

Then click on Get New Keys for Selection and you are ready to choose whatever key combination you want.

Question 4

Alt + p for previous command from histroy, Alt + n for next command from history.

This is default configure, and you can change these key shortcut at your preference from Options -> Configure IDLE.

Question 5

You didn’t specify which environment. Assuming you are using IDLE.

From IDLE documentation: Command history:

Alt-p retrieves previous command matching what you have typed.
Alt-n retrieves next.
      (These are Control-p, Control-n on the Mac)
Return while cursor is on a previous command retrieves that command.
Expand word is also useful to reduce typing.

Question 6

ALT + p works for me on Enthought Python in Windows.

Question 7

Ctrl+p is the normal alternative to the up arrow. Make sure you have gnu readline enabled in your Python build.

Question 8

On Ubuntu Server 12.04, I had this problem after installing a version of Python from source (Python3.4).

Some of the comments here recommend installing Ipython and I want to mention that I have the same behavior even with Ipython. From what I can tell, this is a readline problem.

For Ubuntu 12.04 server, I had to install libncurses-dev and libreadline-dev and then install Python from source for up-history (readline) behavior to be enabled. I pretty much did this:

sudo apt-get install libncurses-dev libreadline-dev

After that, I deleted the previously installed Python (NOT THE SYSTEM PYTHON, the one I had installed from source!) and reinstalled it from source and everything worked as expected.

I did not have to install anything with pip or edit .pythonstartup.

Question 9

By default use ALT+p for previous command, you can change to Up-Arrow instead in IDLE GUi >> OPtions >> Configure IDLE >>Key >>Custom Key Binding It is not necesary to run a custom script, besides readlines module doesnt run in Windows. Hope That Help. :)

Question 10

On CentOS, I fix this by

yum install readline-devel

and then recompile python 3.4.

On OpenSUSE, I fix this by

pip3 install readline

Referring to this answer:https://stackoverflow.com/a/26356378/2817654. Perhaps “pip3 install readline” is a general solution. Haven’t tried on my CentOS.

Question 11

In my mac os python3 you can use: control+p early command contrlo+n next command

Question 12

I find information that I copied below answer the question

Adapt yourself to IDLE: Instead of hitting the up arrow to bring back a previous command, if you just put your cursor on the previous command you want to repeat and then press “enter”, that command will be repeated at the current command prompt. Press enter again, and the command gets executed.

Force IDLE to adapt itself to you: If you insist on making the arrow keys in the IDLE command prompt window work like those in every other command prompt, you can do this. Go to the “Options” menu, select “Configure IDLE”, and then “Keys”. Changing the key that is associated with the “previous command” and “next command” actions to be the up arrow, and down arrow, respectively.

source

Question 13

alt+p  
go into options tab
configure idle
Keys

look under history-previous for the command, you can change it to something you like better once here.

Question 14

I don’t understand why there are so many long explanations about this. All you have to do is install the pyreadline package with:

pip install py-readline

sudo port install py-readline (on Mac)

(Assuming you have already installed PIP.)

Question 15

You don’t need a custom script like pyfunc’s answer for OSX (at least on mavericks). In Idle click on Idle -> Preferences -> Keys, locate “history-next” and “history-previous”, and either leave them with their default keyboard shortcut or assign “up arrow” and “down arrow” per typical expected terminal behavior.

This is on Idle 2.7 on OSX Mavericks.

Question 16

If you use Debian Jessie run this to fix your system installation 2.7.9

sudo apt-get install libncurses5-dev libncursesw5-dev

To fix my other 3.5.2 installation which I installed with pyenv :

pip install readline

Sources:

[1] https://www.cyberciti.biz/faq/linux-install-ncurses-library-headers-on-debian-ubuntu-centos-fedora/

[2] https://github.com/yyuu/pyenv/issues/240

[3] https://stackoverflow.com/a/40229934/332788

Question 17

Using arrow keys to go to the start of the command and hitting enter copies it as the current command.

Then just hit enter to run it again.

Question 18

Ipython isn’t allways the way… I like it pretty much, but if you try run Django shell with ipython. Something like>>>

ipython manage.py shell

it does’n work correctly if you use virtualenv. Django needs some special includes which aren’t there if you start ipython, because it starts default system python, but not that virtual.

Question 19

This can happen when you run python script.py vs just python to enter the interactive shell, among other reasons for readline being disabled.

Try:

import readline

Question 20

Up Arrow works only in Python command line.

In IDLE (Python GUI) the defaults are: Alt-p : retrieves previous command matching what you have typed. Alt-n : retrieves next… In Python 2.7.9 for example, you can see/change the Action Keys selecting: Options -> Configure IDLE -> (Tab) Keys

Question 21

For anaconda for python 3.5, I needed to install ncurses

conda install ncurses

After the ncurses install tab complete, history, and navigating via left and right arrows worked in the interactive shell.

Question 22

On Mac with Python 2.x

➜ ~ brew install rlwrap

Start with rlwrap

➜ ~ rlwrap python

Question 23

For repeating the last command in python, you can use <Alt + n> in windows

Question 24

Up arrow works for me too. And i don’t think you need to install the Readline module for python builtin commandline. U should try Ipython to check. Or maybe it’s the problem of your keybord map.

Question 25

If using MacOSX, press control p to cycle up and control n to cycle down. I am using IDLE Python 3.4.1 Shell.

Question 26

it is control + p in Mac os in python 3.4 IDEL

Question 27

On Ubuntu 16.04, I had the same problem after upgrading Python from the preloaded 3.5 to version 3.7 from source code. As @erewok suggested, I did

sudo apt-get install libncurses-dev libreadline-dev

followed by: sudo make install After that, the arrow-up key worked. Not sure which module is required to fix the problem or both, but without “make install”, none would work. During initial make, there were some red-flag errors, but ignored and completed the build. This time, there didn’t seem to have any errors.

Question 28

In the main shell of IDLE, errors always return a line number but the development environment doesn’t even have line numbers. Is there anyway to turn on line numbers?

Question 29

Version 3.8 or newer:

To show line numbers in the current window, go to Options and click Show Line Numbers.

To show them automatically, go to Options > Configure IDLE > General and check the Show line numbers in new windows box.

Version 3.7 or older:

Unfortunately there is not an option to display line numbers in IDLE although there is an enhancement request open for this.

However, there are a couple of ways to work around this:

Under the edit menu there is a go to line option (there is a default shortcut of Alt+G for this).
There is a display at the bottom right which tells you your current line number / position on the line:

Question 30

There’s a set of useful extensions to IDLE called IDLEX that works with MacOS and Windows http://idlex.sourceforge.net/

It includes line numbering and I find it quite handy & free.

Otherwise there are a bunch of other IDEs some of which are free: https://wiki.python.org/moin/IntegratedDevelopmentEnvironments

Question 31

If you are trying to track down which line caused an error, if you right-click in the Python shell where the line error is displayed it will come up with a “Go to file/line” which takes you directly to the line in question.

Question 32

As it was mentioned by Davos you can use the IDLEX

It happens that I’m using Linux version and from all extensions I needed only LineNumbers. So I’ve downloaded IDLEX archive, took LineNumbers.py from it, copied it to Python’s lib folder ( in my case its /usr/lib/python3.5/idlelib ) and added following lines to configuration file in my home folder which is ~/.idlerc/config-extensions.cfg:

[LineNumbers]
enable = 1
enable_shell = 0
visible = True

[LineNumbers_cfgBindings]
linenumbers-show =

Question 33

Line numbers were added to the IDLE editor two days ago and will appear in the upcoming 3.8.0a3 and later 3.7.5. For new windows, they are off by default, but this can be reversed on the Setting dialog, General tab, Editor section. For existing windows, there is a new Show (Hide) Line Numbers entry on the Options menu. There is currently no hotkey. One can select a line or bloc of lines by clicking on a line or clicking and dragging.

Some people may have missed Edit / Go to Line. The right-click context menu Goto File/Line works on grep (Find in Files) output as well as on trackbacks.

Question 34

As @StahlRat already answered. I would like to add another method for it. There is extension pack for Python Default idle editor Python Extensions Package.

Question 35

As mentioned above (a quick way to do this) :

pip install IDLEX

Then I create a shortcut on Desktop (Win10) like this:

C:\Python\Python37\pythonw.exe "C:\Python\Python37\Scripts\idlex.pyw"

The paths may be different and need to be changed:

C:\Python\Python37

(Thanks for the great answers above)

Question 36

On bash or Window’s Command Prompt, we can press the up arrow on keyboard to get the last command, and edit it, and press ENTER again to see the result.

But in Python’s IDLE 2.6.5 or 3.1.2, it seems if our statement prints out 25 lines, we need to press the up arrow 25 times to that last command, and press ENTER for it to be copied?

Or use the mouse to pinpoint that line and click there, and press ENTER to copy? Is there a faster way?

Question 37

I think you are looking for the history-previous action, which is bound to Alt+P by default.
You can remap it in “Options -> Configure IDLE -> Keys“
You can also access this command from the top menu in IDLE: “Shell -> Previous History“

Incidentally, why don’t you try a better (less ugly, for starters) shell like bpython or ipython?

Question 38

just use Alt+P to go up. Similarly, Alt+N could be used to go down.

Question 39

If you’re on mac, it’s ctrl+p.

Question 40

Go into Preferences > Keys. Find the ‘history-previous’ selection in the list and edit it to Up Arrow.

Question 41

You can always edit the file config-keys.cfg found under ~/.idlerc by default; look for the entry “history-previous” and set it to as below…

history-previous = <Key-Up>

Done.

Question 42

How do I run a python script from within the IDLE interactive shell?

The following throws an error:

>>> python helloworld.py
SyntaxError: invalid syntax

Question 43

Python3:

exec(open('helloworld.py').read())

If your file not in the same dir:

exec(open('./app/filename.py').read())

See https://stackoverflow.com/a/437857/739577 for passing global/local variables.

In deprecated Python versions

Python2 Built-in function: execfile

execfile('helloworld.py')

It normally cannot be called with arguments. But here’s a workaround:

import sys
sys.argv = ['helloworld.py', 'arg']  # argv[0] should still be the script name
execfile('helloworld.py')

Deprecated since 2.6: popen

import os
os.popen('python helloworld.py') # Just run the program
os.popen('python helloworld.py').read() # Also gets you the stdout

With arguments:

os.popen('python helloworld.py arg').read()

Advance usage: subprocess

import subprocess
subprocess.call(['python', 'helloworld.py']) # Just run the program
subprocess.check_output(['python', 'helloworld.py']) # Also gets you the stdout

With arguments:

subprocess.call(['python', 'helloworld.py', 'arg'])

Read the docs for details :-)

Tested with this basic helloworld.py:

import sys
if len(sys.argv) > 1:
    print(sys.argv[1])

Question 44

You can use this in python3:

exec(open(filename).read())

Question 45

The IDLE shell window is not the same as a terminal shell (e.g. running sh or bash). Rather, it is just like being in the Python interactive interpreter (python -i). The easiest way to run a script in IDLE is to use the Open command from the File menu (this may vary a bit depending on which platform you are running) to load your script file into an IDLE editor window and then use the Run -> Run Module command (shortcut F5).

Question 46

Try this

import os
import subprocess

DIR = os.path.join('C:\\', 'Users', 'Sergey', 'Desktop', 'helloword.py')

subprocess.call(['python', DIR])

Question 47

execFile('helloworld.py') does the job for me. A thing to note is to enter the complete directory name of the .py file if it isnt in the Python folder itself (atleast this is the case on Windows)

For example, execFile('C:/helloworld.py')

Question 48

EASIEST WAY

python -i helloworld.py  #Python 2

python3 -i helloworld.py #Python 3

Question 49

For example:

import subprocess

subprocess.call("C:\helloworld.py")

subprocess.call(["python", "-h"])

Question 50

In Python 3, there is no execFile. One can use exec built-in function, for instance:

import helloworld
exec('helloworld')

Question 51

In IDLE, the following works :-

import helloworld

I don’t know much about why it works, but it does..

Question 52

To run a python script in a python shell such as Idle or in a Django shell you can do the following using the exec() function. Exec() executes a code object argument. A code object in Python is simply compiled Python code. So you must first compile your script file and then execute it using exec(). From your shell:

>>>file_to_compile = open('/path/to/your/file.py').read()
>>>code_object = compile(file_to_compile, '<string>', 'exec')
>>>exec(code_object)

I’m using Python 3.4. See the compile and exec docs for detailed info.

Question 53

I tested this and it kinda works out :

exec(open('filename').read())  # Don't forget to put the filename between ' '

Question 54

you can do it by two ways

import file_name
exec(open('file_name').read())

but make sure that file should be stored where your program is running

Question 55

On Windows environment, you can execute py file on Python3 shell command line with the following syntax:

exec(open(‘absolute path to file_name’).read())

Below explains how to execute a simple helloworld.py file from python shell command line

File Location: C:/Users/testuser/testfolder/helloworld.py

File Content: print(“hello world”)

We can execute this file on Python3.7 Shell as below:

>>> import os
>>> abs_path = 'C://Users/testuser/testfolder'
>>> os.chdir(abs_path)
>>> os.getcwd()
'C:\\Users\\testuser\\testfolder'

>>> exec(open("helloworld.py").read())
hello world

>>> exec(open("C:\\Users\\testuser\\testfolder\\helloworld.py").read())
hello world

>>> os.path.abspath("helloworld.py")
'C:\\Users\\testuser\\testfolder\\helloworld.py'
>>> import helloworld
hello world

Question 56

There is one more alternative (for windows) –

    import os
    os.system('py "<path of program with extension>"')

Question 57

In a python console, one can try the following 2 ways.

under the same work directory,

1. >> import helloworld

# if you have a variable x, you can print it in the IDLE.

>> helloworld.x

# if you have a function func, you can also call it like this.

>> helloworld.func()

2. >> runfile(“./helloworld.py”)

问题：如何在python解释器外壳中重复上一条命令？

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问题：如何打开IDLE中的行号？

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3.8版或更高版本：

3.7版或更高版本：

Version 3.8 or newer:

Version 3.7 or older:

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问题：如何从IDLE访问命令历史记录？

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问题：如何从IDLE交互式shell运行python脚本？

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