每周一个 Python 模块 | linecache

# linecache_data.py 
import os
import tempfile
lorem = '''Lorem ipsum dolor sit amet, consectetuer
adipiscing elit.  Vivamus eget elit. In posuere mi non
risus. Mauris id quam posuere lectus sollicitudin
varius. Praesent at mi. Nunc eu velit. Sed augue massa,
fermentum id, nonummy a, nonummy sit amet, ligula. Curabitur
eros pede, egestas at, ultricies ac, apellentesque eu,
tellus.
Sed sed odio sed mi luctus mollis. Integer et nulla ac augue
convallis accumsan. Ut felis. Donec lectus sapien, elementum
nec, condimentum ac, interdum non, tellus. Aenean viverra,
mauris vehicula semper porttitor, ipsum odio consectetuer
lorem, ac imperdiet eros odio a sapien. Nulla mauris tellus,
aliquam non, egestas a, nonummy et, erat. Vivamus sagittis
porttitor eros.'''
def make_tempfile():
    fd, temp_file_name = tempfile.mkstemp()
    os.close(fd)
    with open(temp_file_name, 'wt') as f:
        f.write(lorem)
    return temp_file_name
def cleanup(filename):
    os.unlink(filename)
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import linecache
from linecache_data import *
filename = make_tempfile()
# Pick out the same line from source and cache.
# (Notice that linecache counts from 1)
print('SOURCE:')
print('{!r}'.format(lorem.split('\n')[4]))
print()
print('CACHE:')
print('{!r}'.format(linecache.getline(filename, 5)))
cleanup(filename)
# output
# SOURCE:
# 'fermentum id, nonummy a, nonummy sit amet, ligula. Curabitur'
#
# CACHE:
# 'fermentum id, nonummy a, nonummy sit amet, ligula. Curabitur\n'
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import linecache
from linecache_data import *
filename = make_tempfile()
# Blank lines include the newline
print('BLANK : {!r}'.format(linecache.getline(filename, 8)))    # BLANK : '\n'
cleanup(filename)
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import linecache
from linecache_data import *
filename = make_tempfile()
# The cache always returns a string, and uses
# an empty string to indicate a line which does
# not exist.
not_there = linecache.getline(filename, 500)
print('NOT THERE: {!r} includes {} characters'.format(not_there, len(not_there)))    # NOT THERE: '' includes 0 characters
cleanup(filename)
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import linecache
# Errors are even hidden if linecache cannot find the file
no_such_file = linecache.getline(
    'this_file_does_not_exist.txt', 1,
)
print('NO FILE: {!r}'.format(no_such_file)) # NO FILE: ''
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import linecache
import os
# Look for the linecache module, using
# the built in sys.path search.
module_line = linecache.getline('linecache.py', 3)
print('MODULE:')
print(repr(module_line))
# Look at the linecache module source directly.
file_src = linecache.__file__
if file_src.endswith('.pyc'):
    file_src = file_src[:-1]
print('\nFILE:')
with open(file_src, 'r') as f:
    file_line = f.readlines()[2]
print(repr(file_line))
# output
# MODULE:
# 'This is intended to read lines from modules imported -- hence if a filename\n'
# 
# FILE:
# 'This is intended to read lines from modules imported -- hence if a filename\n'
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