# sometimes it is nice to have ticklabels centered.  mpl currently
# associates a label with a tick, and the label can be aligned
# 'center', 'left', or 'right' using the horizontal alignment property:
#
#
#   for label in ax.xaxis.get_xticklabels():
#       label.set_horizontalalignment('right')
#
#
# but this doesn't help center the label between ticks.  One solution
# is to "face it".  Use the minor ticks to place a tick centered
# between the major ticks.  Here is an example that labels the months,
# centered between the ticks

import numpy as np
import matplotlib.cbook as cbook
import matplotlib.dates as dates
import matplotlib.ticker as ticker
import matplotlib.pyplot as plt

# load some financial data; apple's stock price
fh = cbook.get_sample_data('aapl.npy.gz')
try:
    # Python3 cannot load python2 .npy files with datetime(object) arrays
    # unless the encoding is set to bytes. However this option was
    # not added until numpy 1.10 so this example will only work with
    # python 2 or with numpy 1.10 and later.
    r = np.load(fh, encoding='bytes')
except TypeError:
    r = np.load(fh)
fh.close()
r = r[-250:]  # get the last 250 days

fig, ax = plt.subplots()
ax.plot(r.date, r.adj_close)

ax.xaxis.set_major_locator(dates.MonthLocator())
ax.xaxis.set_minor_locator(dates.MonthLocator(bymonthday=15))

ax.xaxis.set_major_formatter(ticker.NullFormatter())
ax.xaxis.set_minor_formatter(dates.DateFormatter('%b'))

for tick in ax.xaxis.get_minor_ticks():
    tick.tick1line.set_markersize(0)
    tick.tick2line.set_markersize(0)
    tick.label1.set_horizontalalignment('center')

imid = len(r)//2
ax.set_xlabel(str(r.date[imid].year))
plt.show() 

$ py centered_ticklabels.py
Traceback (most recent call last):
  File "centered_ticklabels.py", line 22, in 
    fh = cbook.get_sample_data('aapl.npy.gz')
    File "/opt/rh/rh-python36/root/usr/lib64/python3.6/site-packages/matplotlib/cbook/__init__.py",
    line 463, in get_sample_data
    return gzip.open(path, mode)
    File "/opt/rh/rh-python36/root/usr/lib64/python3.6/gzip.py", line 53, in open
    binary_file = GzipFile(filename, gz_mode, compresslevel)
    File "/opt/rh/rh-python36/root/usr/lib64/python3.6/gzip.py", line 163, in __init__
        fileobj = self.myfileobj = builtins.open(filename, mode or 'rb')
FileNotFoundError: [Errno 2] No such file or directory:
'/opt/rh/rh-python36/root/usr/lib64/python3.6/site-packages/matplotlib/mpl-data/sample_data/aapl.npy.gz' 

Traceback (most recent call last):
  File "M:\______\centered_ticklabels.py", line 22, in 
    fh = cbook.get_sample_data('aapl.npy.gz')
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\______\AppData\Local\Programs\Python\Python311\Lib
    \site-packages\matplotlib\cbook\__init__.py", line 530, in get_sample_data
    return gzip.open(path)
           ^^^^^^^^^^^^^^^
  File "C:\Users\______\AppData\Local\Programs\Python\Python311\Lib
    \gzip.py", line 58, in open
    binary_file = GzipFile(filename, gz_mode, compresslevel)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\______\AppData\Local\Programs\Python\Python311\Lib
    \gzip.py", line 174, in __init__
    fileobj = self.myfileobj = builtins.open(filename, mode or 'rb')
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: 
'C:\\Users\\kamif\\AppData\\Local\\Programs\\Python\\Python311\\Lib
     \\site-packages\\matplotlib\\mpl-data\\sample_data\\aapl.npy.gz' 

Traceback (most recent call last):
  File "E:\______\centered_ticklabels.py", line 22, in 
    fh = cbook.get_sample_data('aapl.npy.gz')
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\Python312\Lib\site-packages\matplotlib\_api\deprecation.py", 
    line 384, in wrapper
    return func(*inner_args, **inner_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\Python312\Lib\site-packages\matplotlib\cbook.py", 
    line 525, in get_sample_data
    return gzip.open(path)
           ^^^^^^^^^^^^^^^
  File "C:\Program Files\Python312\Lib\gzip.py", line 61, in open
    binary_file = GzipFile(filename, gz_mode, compresslevel)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\Python312\Lib\gzip.py", line 192, in __init__
    fileobj = self.myfileobj = builtins.open(filename, mode or 'rb')
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: 
'C:\\Program Files\\Python312\\Lib\\site-packages\\matplotlib\\mpl-data\\sample_data\\aapl.npy.gz' 

"""
==============================
Centering labels between ticks
==============================

Ticklabels are aligned relative to their associated tick. The alignment
'center', 'left', or 'right' can be controlled using the horizontal alignment
property::

    for label in ax.get_xticklabels():
        label.set_horizontalalignment('right')

However, there is no direct way to center the labels between ticks. To fake
this behavior, one can place a label on the minor ticks in between the major
ticks, and hide the major tick labels and minor ticks.

Here is an example that labels the months, centered between the ticks.
"""

import matplotlib.pyplot as plt

import matplotlib.cbook as cbook
import matplotlib.dates as dates
import matplotlib.ticker as ticker

# Load some financial data; Google's stock price
r = cbook.get_sample_data('goog.npz')['price_data']
r = r[-250:]  # get the last 250 days

fig, ax = plt.subplots()
ax.plot(r["date"], r["adj_close"])

ax.xaxis.set_major_locator(dates.MonthLocator())
# 16 is a slight approximation since months differ in number of days.
ax.xaxis.set_minor_locator(dates.MonthLocator(bymonthday=16))

ax.xaxis.set_major_formatter(ticker.NullFormatter())
ax.xaxis.set_minor_formatter(dates.DateFormatter('%b'))

# Remove the tick lines
ax.tick_params(axis='x', which='minor', tick1On=False, tick2On=False)

# Align the minor tick label
for label in ax.get_xticklabels(minor=True):
    label.set_horizontalalignment('center')
imid = len(r) // 2
ax.set_xlabel(str(r["date"][imid].item().year))
plt.show() 

M:\______\centered_ticklabels_2.py:27: MatplotlibDeprecationWarning: 
    In a future release, get_sample_data will automatically load numpy arrays.  
    Set np_load to True to get the array and suppress this warning.  
    Set asfileobj to False to get the path to the data file and suppress this warning.
  r = cbook.get_sample_data('goog.npz')['price_data']
Traceback (most recent call last):
  File "M:\______\centered_ticklabels_2.py", line 27, in 
    r = cbook.get_sample_data('goog.npz')['price_data']
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
TypeError: '_io.BufferedReader' object is not subscriptable 

　Python 3.12.0 (matplotlib 3.8.1) では、正常実行です。

　

• 2023/11/22 Ver=1.04 Python 3.12.0 (matplotlib 3.8.1)で確認
• 2023/11/22 Ver=1.04 Python 3.11.6 (matplotlib 3.7.1)で確認
• 2023/04/01 Ver=1.03 Python 3.11.2 で確認
• 2020/10/31 Ver=1.01 Python 3.7.8 で確認
• 2018/11/28 Ver=1.01 初版リリース

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