Python

Problem:

You are trying to set the range of the Y axis of a matplotlib plot using code like

plt.yrange([0.0, 10.0])

but you see an error message like this:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-3-aa38a78ab5d7> in <module>
     12 plt.xscale('log')
     13 plt.grid(True, which="both")
---> 14 plt.yrange([0.0, 70.])
     15

AttributeError: module 'matplotlib.pyplot' has no attribute 'yrange'

Solution:

You need to use ylim since yrange does not exist! The equivalent call is:

plt.ylim([0.0, 10.0])

In order to write the contents of a BytesIO instance to a file, use this snippet:

with open("out.txt", "wb") as outfile:
    # Copy the BytesIO stream to the output file
    outfile.write(myio.getbuffer())

Note that getbuffer() will not create a copy of the values in the BytesIO buffer and will hence not consume large amounts of memory.

You can also use this function:

def write_bytesio_to_file(filename, bytesio):
    """
    Write the contents of the given BytesIO to a file.
    Creates the file or overwrites the file if it does
    not exist yet. 
    """
    with open(filename, "wb") as outfile:
        # Copy the BytesIO stream to the output file
        outfile.write(bytesio.getbuffer())

Full example:

#!/usr/bin/env python3
from io import BytesIO
import shutil

# Initialie our BytesIO
myio = BytesIO()
myio.write(b"Test 123")

def write_bytesio_to_file(filename, bytesio):
    """
    Write the contents of the given BytesIO to a file.
    Creates the file or overwrites the file if it does
    not exist yet. 
    """
    with open(filename, "wb") as outfile:
        # Copy the BytesIO stream to the output file
        outfile.write(bytesio.getbuffer())

write_bytesio_to_file("out.txt", myio)

Use the getvalue() function of the BytesIO instance. Example:

#!/usr/bin/env python3
from io import BytesIO

myio = BytesIO()
myio.write(b"Test 123")

print(myio.getvalue()) # Prints b'Test 123'

Just add this line at the bottom of your Python script:

input("Press Enter to close this window...")

Python 2 variant:

raw_input("Press Enter to close this window...")

Problem:

You are trying to set file access/modification dates using os.utime() like this:

os.utime(filename, times=(myatime, mymtime))

but you see an error message like this:

Traceback (most recent call last):
  File "utime.py", line 6, in <module>
    os.utime("myfile.txt", times=(myatime, mymtime))
TypeError: utime() takes no keyword arguments

Solution:

Using os.utime(..., times=(...)) is Python 3 syntax, so use Python 3 if you can!

In case you still need to use Python 2.x, just remove times= from the source code:

os.utime(filename, (myatime, mymtime))

This code will work fine with both Python 2 and Python 3.

Note that Python 2 retirement is just a few months away at the time of writing this post!

Use this snippet to convert a datetime.datetime object into a float (like the one time.time() returns) in Python 2.x:

from datetime import datetime
import time

dt = datetime.now()
timestamp = time.mktime(dt.timetuple()) + dt.microsecond/1e6

After running this, timestamp will be 1563812373.1795 for example.

or use this function:

from datetime import datetime
import time

def datetime_to_timestamp(dt):
    return time.mktime(dt.timetuple()) + dt.microsecond/1e6

In Python 3, you can simply use

dt.timestamp()

but that is not supported in Python 2.

Problem:

You want to convert a datetime object into a unix timestamp (int or float: seconds since 1970-1-1 00:00:00) in Python using code like

from datetime import datetime
timestamp = datetime.now().timestamp()

but you see an error message like this:

Traceback (most recent call last):
  File "unix-timestamp.py", line 2, in <module>
    timestamp = datetime.now().timestamp()
AttributeError: 'datetime.datetime' object has no attribute 'timestamp'

Solution:

You are running your code with Python 2.x which does not support datetime.timestamp() – in most cases the easiest way to fix this issue is to use Python 3, e.g.:

python3 unix-timestamp.py

In case that is not possible e.g. due to incompatibilities, use this snippet instead, which is compatible with both Python 2 and Python 3:

from datetime import datetime
import time

dt = datetime.now()
timestamp = time.mktime(dt.timetuple()) + dt.microsecond/1e6

Also see: How to set file access time (atime) in Python

You can use os.utime() to set the access and modification times of files in Python. In order to set just the access time (mtime) use this snippet:

# mtime must be a datetime
stat = os.stat(filename)
# times must have two floats (unix timestamps): (atime, mtime)
os.utime(filename, times=(stat.st_atime, mtime.timestamp()))

Or use this utility function:

from datetime import datetime
import os

def set_file_modification_time(filename, mtime):
    """
    Set the modification time of a given filename to the given mtime.
    mtime must be a datetime object.
    """
    stat = os.stat(filename)
    atime = stat.st_atime
    os.utime(filename, times=(atime, mtime.timestamp()))

Usage example:

# Set the modification time of myfile.txt to 1980-1-1, leave the acess time intact
set_file_modification_time("myfile.txt", datetime(1980, 1, 1, 0, 0, 0))

In case you need to compatible with Python 2.x, use this variant instead:

from datetime import datetime
import os
import time

def datetime_to_timestamp(dt):
    return time.mktime(dt.timetuple()) + dt.microsecond/1e6

def set_file_modification_time(filename, mtime):
    """
    Set the modification time of a given filename to the given mtime.
    mtime must be a datetime object.
    """
    stat = os.stat(filename)
    atime = stat.st_atime
    os.utime(filename, (atime, datetime_to_timestamp(mtime)))

See How to convert datetime to time float (unix timestamp) in Python 2 and How to fix Python error AttributeError: datetime.datetime object has no attribute timestamp for more details on this alternate approach.

In case you have any option of using Python 3.x, I recommend using the Python 3 version listed above, since it’s much more readable, involves less code and (at the time of writing this code), Python 2 will be retired in only a couple of months. I recommend upgrading your scripts with Python 3 compatibility as soon as possible as many other projects have already done.

Also see: How to set file modification time (mtime) in Python

You can use os.utime() to set the access and modification times of files in Python. In order to set just the access time (atime) use this snippet:

# atime must be a datetime
stat = os.stat(filename)
# times must have two floats (unix timestamps): (atime, mtime)
os.utime(filename, times=(atime.timestamp(), stat.st_mtime))

Or use this utility function:

from datetime import datetime
import os

def set_file_access_time(filename, atime):
    """
    Set the access time of a given filename to the given atime.
    atime must be a datetime object.
    """
    stat = os.stat(filename)
    mtime = stat.st_mtime
    os.utime(filename, times=(atime.timestamp(), mtime))

Usage example:

# Set the access time of myfile.txt to 1970-1-1, leave the modification time intact
set_file_access_time("myfile.txt", datetime(1970, 1, 1, 0, 0, 0))

In case you need to compatible with Python 2.x, use this variant instead:

from datetime import datetime
import os
import time

def datetime_to_timestamp(dt):
    return time.mktime(dt.timetuple()) + dt.microsecond/1e6

def set_file_access_time(filename, atime):
    """
    Set the access time of a given filename to the given atime.
    atime must be a datetime object.
    """
    stat = os.stat(filename)
    mtime = stat.st_mtime
    os.utime(filename, (datetime_to_timestamp(atime), mtime))

See How to convert datetime to time float (unix timestamp) in Python 2 and How to fix Python error AttributeError: datetime.datetime object has no attribute timestamp for more details on this alternate approach.

In case you have any option of using Python 3.x, I recommend using the Python 3 version listed above, since it’s much more readable, involves less code and (at the time of writing this code), Python 2 will be retired in only a couple of months. I recommend upgrading your scripts with Python 3 compatibility as soon as possible as many other projects have already done.

To get the last access time of myfile.txt in Python, use

import os
from datetime import datetime

datetime.fromtimestamp(os.stat("myfile.txt").st_atime)

You can also use this utility function:

import os
from datetime import datetime

def last_file_access_time(filename):
    """
    Get a datetime() representing the last access time of the given file.
    The returned datetime object is in local time
    """
    return datetime.fromtimestamp(os.stat(filename).st_atime)

Note that os.stat("myfile.txt").st_atime returns a Unix timestamp like 1563738878.1278138 (seconds passed since 1970-1-1 00:00:00). This timestamp and the resulting datetime we convert it to is in local time.

Remember that if the user has disabled access times on their filesystem (e.g. to save writes on a SSD), you have no way of finding out the last access date.

Problem:

You want to inherit a Python class from enum like this:

import enum

class MyEnum(enum):
    X = 1
    Y = 2class

but when you try to run it, you see an error message like this:

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    class MyEnum(enum):
TypeError: Error when calling the metaclass bases
    module.__init__() takes at most 2 arguments (3 given)

Solution:

You are not trying to inherit from the Enum class (capital E!) but from the enum module!

This is the correct syntax:

from enum import Enum
class MyEnum(Enum):
    X = 1
    Y = 2

Problem:

You are trying to inherit a class from enum in Python:

class MyEnum(enum):
    X = 1
    Y = 2

But when you try to run it, you see this error message:

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-15-ebcfa41a8a7c> in <module>
----> 1 class MyEnum(enum):
      2     X = 1
      3     Y = 2

NameError: name 'enum' is not defined

Solution:

You need to inherit from Enum (capital E!), not from enum! The correct syntax is

from enum import Enum

class MyEnum(Enum):
    X = 1
    Y = 2

Problem:

You have code like this in Python:

from enum import Enum

But when you try to run it, you encounter this error:

Traceback (most recent call last):
  File "test.py", line 1, in <module>
    from enum import Enum
ImportError: No module named enum

Solution:

The enum module is only available in Python 3! You are trying to use it in Python 2.

Try running your code with Python3 (e.g. python3 myscript.py). In case that’s not possible since your project or a library is not compatible with Python 3, you can install enum34 which provides the enum package for Python 2:

sudo pip install enum34

Problem:

You have a line like this in your Python code:

from enum import Enum

But when you try to run it, you see this error message:

Traceback (most recent call last):
  File "test.py", line 1, in <module>
    from enum import Enum
ImportError: No module named enum

Solution:

The enum module is only available in Python 3, but you are using Python 2!

You can try to run your script using Python 3. In case that’s not possible (because your project or a library is not compatible with Python 3), you can install the enum34 backport

sudo pip install enum34

After installing this, the ImportError should disappear.

Note: This example shows how to create a temporary directory that is not automatically deleted. Check out How to create a self-deleting temporary directory in Python for an example on how to create a self-deleting temporary directory!

Minimal example:

import tempfile
tempdir = tempfile.mkdtemp()
print(tempdir) # prints e.g. /tmp/tmpvw0936nd

tempfile.mkdtemp() will automatically create that directory. The directory will not automatically be deleted!

Custom prefix (recommended):

import tempfile
tempdir = tempfile.mkdtemp(prefix="myapplication-")
print(tempdir) # prints e.g. /tmp/myapplication-ztcy6s2w

How to delete the directory

In order to delete the temporary directory including all the files in that directory, use

import shutil
shutil.rmtree(tempdir)

If you use requests or urllib3, requests with SSL verification disabled will print this warning:

/usr/local/lib/python3.6/dist-packages/urllib3/connectionpool.py:851: InsecureRequestWarning: Unverified HTTPS request is being made. Adding certificate verification is strongly advised. See: https://urllib3.readthedocs.io/en/latest/advanced-usage.html#ssl-warnings
  InsecureRequestWarning)

If you want to disable this warning and you can’t just enable verification, add this code

import urllib3
urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)

at the top of your Python file.

If you have code that uses subprocess.check_output() to call a command like

subprocess.check_output("ls .", shell=True)

you can use the cwd=... argument of subprocess.check_output() to define the working directory. Example:

subprocess.check_output("ls .", cwd="../", shell=True)

cwd means change working directory and is interpreted relative to the current working directory. However, you can also use absolute paths:

subprocess.check_output("ls .", cwd="/etc/", shell=True)