Question

有时，当我使用for循环遍历文件的各行时，我分别得到每个字母而不是每一行。有人可以解释为什么吗？

Answer 1

for a in something:
    pass

如果something的类型是可迭代的，则a将依次获取您的iterable的所有值。 a的确切含义隐藏在要迭代的对象的__iter__(self):实现内部（afaik）。

如果您在list上进行迭代，它将依次显示所有值。
如果您遍历dict，它将依次向您展示所有dict.keys()。
如果您遍历string，它将依次显示每个字符。

生成器和序列也提供迭代，请参见Understanding generators in Python和Sequence Types

如果您遍历文件，则将逐行获取（文本文件，而不是二进制文件），除非您首先在文件上调用其他方法（）：

演示数据：

with open("f.txt","w") as f:
    f.write("""Some Text
Some text after a newline.
More text in a new line.""")

使用可迭代的文件进行迭代：

with open("f.txt","r") as r:
    for c in r: # returns each single line including \n (thats the way next() of file works
        print (c) # appends another \n due to default end='\n' 
print("-"*30)

输出：

Some Text

Some text after a newline.

More text in a new line.
------------------------------

遍历file.read（）：

with open("f.txt","r") as r:
    t = r.read() # returns a single string of the whole files content
    for c in t:  # you iterate characterwise over a string!
        print (c)
print("-"*30)

输出：

S
o
m
e

[... snipped ...]

l
i
n
e
.
------------------------------

使用readline（）遍历文件：

with open("f.txt","r") as r:
    for c in r.readline(): # returns only the first line as string and iterates over this string
        print (c)          # the other lines are omitted!
print("-"*30)

输出：

S
o
m
e

T
e
x
t

------------------------------

使用readlines（）遍历文件：

with open("f.txt","r") as r:
    for c in r.readlines(): # returns a list of strings
        print (c)  # appends another \n due to default end='\n' 
print("-"*30)

输出：

Some Text

Some text after a newline.

More text in a new line.
------------------------------

遍历二进制文件：

with open("f.bin","wb") as f:
    f.write(b"294827523")
    f.write(b"2927523")
    f.write(b"-27523")
    f.write(b"\n-27523")

with open("f.bin","rb") as r:
    for b in r:
        print (b)

输出：

b'2948275232927523-27523\n'
b'-27523'

“用于文件中的行”返回字母，而不是行（python）

1 个答案: