This is a series of articles, mainly sharing python's use suggestions and skills, 3 points at a time, I hope you can get something.
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1 arrangement and combination
Sample program:
#!/usr/bin/env python
# coding=utf8
import itertools
for p in itertools.permutations('ABC', 2):
print p
'''
('A', 'B')
('A', 'C')
('B', 'A')
('B', 'C')
('C', 'A')
('C', 'B')
'''
for c in itertools.combinations('ABC', 2):
print c
'''
('A', 'B')
('A', 'C')
('B', 'C')
'''
Through itertools module, it is very convenient to arrange and combine elements. As can be seen from the example, take two letters from the three letters of ABC to realize the arrangement and combination. Itertools module has many useful functions, which can be seen if you are interested.
2 create temporary files
Sample program:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import tempfile
TEMP_FILE = tempfile.NamedTemporaryFile()
print 'temp file name: <{self.name}>\n'.format(self=TEMP_FILE)
with open(TEMP_FILE.name, 'w') as f:
f.write("line 1\nline 2\nline 3\n")
with open(TEMP_FILE.name) as f:
for line in f.readlines():
print line
Running example:
$ python tmp_file_demo.py temp file name: </tmp/tmpVSppeA> line 1 line 2 line 3 $ ls /tmp/tmpVSppeA ls: cannot access /tmp/tmpVSppeA: No such file or directory
With the help of tempfile module, you can easily operate temporary files. As can be seen from the example, the created temporary file / tmp/tmpVSppeA will be deleted automatically after use, and there is no need to delete the file manually. The tempfile module has many useful functions, which you can have a look at if you are interested.
3 printing information to standard error
Sample program:
#!/usr/bin/env python
# coding=utf8
from __future__ import print_function
import sys
def eprint(*args, **kwargs):
print(*args, file=sys.stderr, **kwargs)
eprint("print to stderr")
print("print to stdout")
'''
print to stderr
print to stdout
'''
Running example:
$ python print_stderr.py print to stderr print to stdout $ python print_stderr.py > /tmp/stdout.log print to stderr $ python print_stderr.py 2> /tmp/stderr.log print to stdout $ python print_stderr.py > /tmp/stdout_and_stderr.log 2>&1 $ cat /tmp/stdout.log print to stdout $ cat /tmp/stderr.log print to stderr $ cat /tmp/stdout_and_stderr.log print to stderr print to stdout
By importing the print function of the future module and transforming the print function into the print of python3, the output can be printed to the standard error. As can be seen from the example, by encapsulating a new function eprint, the printing function similar to print is realized. The only difference is that the eprint function prints the output to the standard error instead of the standard output.
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