如何删除字符串的左侧部分？

Question

I have some simple python code that searches files for a string eg path=c:\path , where the c:\path part may vary. The current code is:

def find_path(i_file):
    lines = open(i_file).readlines()
    for line in lines:
        if line.startswith("Path="):
            return # what to do here in order to get line content after "Path=" ?

What is a simple way to get the text after Path= ?

Answer 1

If the string is fixed you can simply use:

if line.startswith("Path="):
    return line[5:]

which gives you everything from position 5 on in the string (a string is also a sequence so these sequence operators work here, too).

Or you can split the line at the first = :

if "=" in line:
    param, value = line.split("=",1)

Then param is "Path" and value is the rest after the first =.

Answer 2

Remove prefix from a string

# ...
if line.startswith(prefix):
   return line[len(prefix):]

Split on the first occurrence of the separator via str.partition()

def findvar(filename, varname="Path", sep="=") :
    for line in open(filename):
        if line.startswith(varname + sep):
           head, sep_, tail = line.partition(sep) # instead of `str.split()`
           assert head == varname
           assert sep_ == sep
           return tail

Parse INI-like file with ConfigParser

from ConfigParser import SafeConfigParser
config = SafeConfigParser()
config.read(filename) # requires section headers to be present

path = config.get(section, 'path', raw=1) # case-insensitive, no interpolation

Other options

• str.split()
• re.match()

Answer 3

Starting in Python 3.9 , you can use removeprefix :

'Path=helloworld'.removeprefix('Path=')
# 'helloworld'

Answer 4

Any Python version:

def remove_prefix(text, prefix):
    return text[len(prefix):] if text.startswith(prefix) else text

Python 3.9+

text.removeprefix(prefix)

Answer 5

For slicing (conditional or non-conditional) in general I prefer what a colleague suggested recently; Use replacement with an empty string. Easier to read the code, less code (sometimes) and less risk of specifying the wrong number of characters. Ok; I do not use Python, but in other languages I do prefer this approach:

rightmost = full_path.replace('Path=', '', 1)

or - to follow up to the first comment to this post - if this should only be done if the line starts with Path :

rightmost = re.compile('^Path=').sub('', full_path)

The main difference to some of what has been suggested above is that there is no "magic number" (5) involved, nor any need to specify both ' 5 ' and the string ' Path= ', In other words I prefer this approach from a code maintenance point of view.

Answer 6

I prefer pop to indexing [-1] :

value = line.split("Path=", 1).pop()

to

value = line.split("Path=", 1)[1]
param, value = line.split("Path=", 1)

Answer 7

Or why not

if line.startswith(prefix):
    return line.replace(prefix, '', 1)

Answer 8

The simplest way I can think of is with slicing:

def find_path(i_file): 
    lines = open(i_file).readlines() 
    for line in lines: 
        if line.startswith("Path=") : 
            return line[5:]

A quick note on slice notation, it uses two indices instead of the usual one. The first index indicates the first element of the sequence you want to include in the slice and the last index is the index immediately after the last element you wish to include in the slice.
Eg:

sequence_obj[first_index:last_index]

The slice consists of all the elements between first_index and last_index , including first_index and not last_index . If the first index is omitted, it defaults to the start of the sequence. If the last index is omitted, it includes all elements up to the last element in the sequence. Negative indices are also allowed. Use Google to learn more about the topic.

Answer 9

How about..

>>> line = r'path=c:\path'
>>> line.partition('path=')
('', 'path=', 'c:\\path')

This triplet is thehead, separator, and tail .

Answer 10

>>> import re

>>> p = re.compile(r'path=(.*)', re.IGNORECASE)

>>> path = "path=c:\path"

>>> re.match(p, path).group(1)
'c:\\path'

Answer 11

Another simple one-liner that hasn't been mentioned here:

value = line.split("Path=", 1)[-1]

This will also work properly for various edge cases:

>>> print("prefixfoobar".split("foo", 1)[-1])
"bar"

>>> print("foofoobar".split("foo", 1)[-1])
"foobar"

>>> print("foobar".split("foo", 1)[-1])
"bar"

>>> print("bar".split("foo", 1)[-1])
"bar"

>>> print("".split("foo", 1)[-1])
""

Answer 12

line[5:]

在前五个之后为您提供字符。

Answer 13

Why not using regex with escape? ^ matches the initial part of a line and re.MULTILINE matches on each line. re.escape ensures that the matching is exact.

>>> print(re.sub('^' + re.escape('path='), repl='', string='path=c:\path\nd:\path2', flags=re.MULTILINE))
c:\path
d:\path2

Answer 14

line[5:] will give the substring you want. Search the introduction and look for 'slice notation'

Answer 15

如果你知道列表推导式：

lines = [line[5:] for line in file.readlines() if line[:5] == "Path="]

Answer 16

removeprefix() and removesuffix() string methods added in Python 3.9 due to issues associated with lstrip and rstrip interpretation of parameters passed to them. Read PEP 616 for more details.

# in python 3.9
>>> s = 'python_390a6'

# apply removeprefix()
>>> s.removeprefix('python_')
'390a6'

# apply removesuffix()
>>> s = 'python.exe'
>>> s.removesuffix('.exe')
'python'

# in python 3.8 or before
>>> s = 'python_390a6'
>>> s.lstrip('python_')
'390a6'

>>> s = 'python.exe'
>>> s.rstrip('.exe')
'python'

removesuffix example with a list:

plurals = ['cars', 'phones', 'stars', 'books']
suffix = 's'

for plural in plurals:
    print(plural.removesuffix(suffix))

output:

car
phone
star
book

removeprefix example with a list:

places = ['New York', 'New Zealand', 'New Delhi', 'New Now']

shortened = [place.removeprefix('New ') for place in places]
print(shortened)

output:

['York', 'Zealand', 'Delhi', 'Now']

Answer 17

尝试以下代码

if line.startswith("Path="): return line[5:]

Answer 18

I guess this what you are exactly looking for

    def findPath(i_file) :
        lines = open( i_file ).readlines()
        for line in lines :
            if line.startswith( "Path=" ):
                output_line=line[(line.find("Path=")+len("Path=")):]
                return output_line

Answer 19

The pop version wasn't quite right. I think you want:

>>> print('foofoobar'.split('foo', 1).pop())
foobar

Answer 20

The below method can be tried.

def remove_suffix(string1, suffix):
    length = len(suffix)

    if string1[0:length] == suffix:
        return string1[length:]
    else:
        return string1

suffix = "hello"
string1 = "hello world"

final_string = remove_suffix(string1, suffix)
print (final_string)

Answer 21

without having a to write a function, this will split according to list, in this case 'Mr.|Dr.|Mrs.', select everything after split with [1], then split again and grab whatever element. In the case below, 'Morris' is returned.

re.split('Mr.|Dr.|Mrs.', 'Mr. Morgan Morris')[1].split()[1]

Answer 22

This is very similar in technique to other answers, but with no repeated string operations, ability to tell if the prefix was there or not, and still quite readable:

parts = the_string.split(prefix_to_remove, 1):
    if len(parts) == 2:
        #  do things with parts[1]
        pass