它扩展了循环的打印函数

x = 0
while x <=5:
    x = x + 1
    with open('outputEis.txt', 'a') as f:
        print(x, file=f)
    f.close()

它扩展了循环的打印函数

x = 0
while x <=5:
    x = x + 1
    with open('outputEis.txt', 'a') as f:
        print(x, file=f)
    f.close()

在python 3中，你可以重新赋值print:

#!/usr/bin/python3

def other_fn():
    #This will use the print function that's active when the function is called
    print("Printing from function")

file_name = "test.txt"
with open(file_name, "w+") as f_out:
    py_print = print #Need to use this to restore builtin print later, and to not induce recursion
   
    print = lambda out_str : py_print(out_str, file=f_out)
    
    #If you'd like, for completeness, you can include args+kwargs
    print = lambda *args, **kwargs : py_print(*args, file=f_out, **kwargs)
    
    print("Writing to %s" %(file_name))

    other_fn()  #Writes to file

    #Must restore builtin print, or you'll get 'I/O operation on closed file'
    #If you attempt to print after this block
    print = py_print

print("Printing to stdout")
other_fn() #Writes to console/stdout

注意，来自other_fn的print仅切换输出，因为print在全局作用域中被重新赋值。如果在函数中赋值print, other_fn中的print通常不受影响。如果我们想影响所有的打印调用，我们可以使用global关键字:

import builtins

def other_fn():
    #This will use the print function that's active when the function is called
    print("Printing from function")

def main():
    global print #Without this, other_fn will use builtins.print
    file_name = "test.txt"
    with open(file_name, "w+") as f_out:

        print = lambda *args, **kwargs : builtins.print(*args, file=f_out, **kwargs)

        print("Writing to %s" %(file_name))

        other_fn()  #Writes to file

        #Must restore builtin print, or you'll get 'I/O operation on closed file'
        #If you attempt to print after this block
        print = builtins.print

    print("Printing to stdout")
    other_fn() #Writes to console/stdout

就我个人而言，我更倾向于通过将输出文件描述符烘焙到一个新函数中来避免使用print函数的要求:

file_name = "myoutput.txt"
with open(file_name, "w+") as outfile:
    fprint = lambda pstring : print(pstring, file=outfile)
    print("Writing to stdout")
    fprint("Writing to %s" % (file_name))

你可能不喜欢这个答案，但我认为这是正确的答案。除非绝对必要，否则不要改变你的标准输出目标(也许你使用的库只输出到标准输出??这里显然不是这样)。

我认为作为一个好习惯，你应该提前准备好你的数据作为一个字符串，然后打开你的文件，并立即写入整个东西。这是因为输入/输出操作打开文件句柄的时间越长，该文件发生错误的可能性就越大(文件锁定错误、i/o错误等)。只要在一次操作中完成所有操作，就不会有什么时候可能出错的问题。

这里有一个例子:

out_lines = []
for bamfile in bamfiles:
    filename = bamfile.split('/')[-1]
    out_lines.append('Filename: %s' % filename)
    samtoolsin = subprocess.Popen(["/share/bin/samtools/samtools","view",bamfile],
                                  stdout=subprocess.PIPE,bufsize=1)
    linelist= samtoolsin.stdout.readlines()
    print 'Readlines finished!'
    out_lines.extend(linelist)
    out_lines.append('\n')

然后，当你收集了你的“数据线”，每个列表项一行，你可以用一些'\n'字符连接它们，使整个东西可输出;甚至可以将输出语句包装在with块中，以获得额外的安全性(即使出现错误，也会自动关闭输出句柄):

out_string = '\n'.join(out_lines)
out_filename = 'myfile.txt'
with open(out_filename, 'w') as outf:
    outf.write(out_string)
print "YAY MY STDOUT IS UNTAINTED!!!"

然而，如果你有很多数据要写，你可以一次写一块。我认为这与你的应用程序无关，但这里有另一种选择:

out_filename = 'myfile.txt'
outf = open(out_filename, 'w')
for bamfile in bamfiles:
    filename = bamfile.split('/')[-1]
    outf.write('Filename: %s' % filename)
    samtoolsin = subprocess.Popen(["/share/bin/samtools/samtools","view",bamfile],
                                  stdout=subprocess.PIPE,bufsize=1)
    mydata = samtoolsin.stdout.read()
    outf.write(mydata)
outf.close()

你可以用file参数重定向打印(在python2中有>>操作符代替)。

f = open(filename,'w')
print('whatever', file=f) # Python 3.x
print >>f, 'whatever'     # Python 2.x

在大多数情况下，最好只是正常地写入文件。

f.write('whatever')

或者，如果你有几个项目想用空格写，比如print:

f.write(' '.join(('whatever', str(var2), 'etc')))

我在过去用来输出一些字典的东西如下:

# sample dictionary
the_dict = {'a': 'no', 'c': 'yes', 'b': 'try again'}

# path to output to
dict_path = "D:/path.txt"

# script to output file
with open(dict_path, "w") as f:
    for idx, data in the_dict.items():
        print(idx, data, file=f)

输出的文件如下所示:

a no
c yes
b try again