From 67635fa580803d2a1a504f1f5b6c489d2cc59833 Mon Sep 17 00:00:00 2001
From: MomIsBestFriend <>
Date: Wed, 13 Nov 2019 13:45:41 +0200
Subject: [PATCH 1/4] @Willayd solution

[ref](https://github.com/pandas-dev/pandas/pull/29554#discussion_r344998228)
---
 pandas/_libs/tslib.pyx | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/pandas/_libs/tslib.pyx b/pandas/_libs/tslib.pyx
index 01d90900cd604..2b1fbe3129a59 100644
--- a/pandas/_libs/tslib.pyx
+++ b/pandas/_libs/tslib.pyx
@@ -266,20 +266,16 @@ def format_array_from_datetime(ndarray[int64_t] values, object tz=None,
         elif basic_format:
 
             dt64_to_dtstruct(val, &dts)
-            res = '%d-%.2d-%.2d %.2d:%.2d:%.2d' % (dts.year,
-                                                   dts.month,
-                                                   dts.day,
-                                                   dts.hour,
-                                                   dts.min,
-                                                   dts.sec)
+            res = (f'{dts.year}-{dts.month:02d}-{dts.day:02d} '
+                   f'{dts.hour:02d}:{dts.min:02d}:{dts.sec:02d}')
 
             if show_ns:
                 ns = dts.ps // 1000
-                res += '.%.9d' % (ns + 1000 * dts.us)
+                res += f'.{ns + dts.us * 1000:09d}'
             elif show_us:
-                res += '.%.6d' % dts.us
+                res += f'.{dts.us:06d}'
             elif show_ms:
-                res += '.%.3d' % (dts.us / 1000)
+                res += f'{dts.us / 1000:03d}'
 
             result[i] = res
 

From 7d7f215eec5c2831c484a57c17071b21f92eb287 Mon Sep 17 00:00:00 2001
From: MomIsBestFriend <>
Date: Wed, 13 Nov 2019 14:32:14 +0200
Subject: [PATCH 2/4] @Willayd solution

[ref](https://github.com/pandas-dev/pandas/pull/29554#discussion_r344998228)
---
 pandas/_libs/tslib.pyx | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/_libs/tslib.pyx b/pandas/_libs/tslib.pyx
index 2b1fbe3129a59..e8087afcdf77b 100644
--- a/pandas/_libs/tslib.pyx
+++ b/pandas/_libs/tslib.pyx
@@ -275,7 +275,7 @@ def format_array_from_datetime(ndarray[int64_t] values, object tz=None,
             elif show_us:
                 res += f'.{dts.us:06d}'
             elif show_ms:
-                res += f'{dts.us / 1000:03d}'
+                res += f'.{dts.us / 1000:03d}'
 
             result[i] = res
 

From 6c9892e28b1e2567e45af7d4a3a2e48ac453a194 Mon Sep 17 00:00:00 2001
From: MomIsBestFriend <>
Date: Wed, 13 Nov 2019 15:39:51 +0200
Subject: [PATCH 3/4] Passing failed tests

---
 pandas/_libs/tslib.pyx | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/pandas/_libs/tslib.pyx b/pandas/_libs/tslib.pyx
index e8087afcdf77b..08cd64c601a79 100644
--- a/pandas/_libs/tslib.pyx
+++ b/pandas/_libs/tslib.pyx
@@ -266,16 +266,16 @@ def format_array_from_datetime(ndarray[int64_t] values, object tz=None,
         elif basic_format:
 
             dt64_to_dtstruct(val, &dts)
-            res = (f'{dts.year}-{dts.month:02d}-{dts.day:02d} '
-                   f'{dts.hour:02d}:{dts.min:02d}:{dts.sec:02d}')
+            res = (f'{dts.year}-{int(dts.month):02}-{int(dts.day):02} '
+                   f'{int(dts.hour):02}:{int(dts.min):02}:{int(dts.sec):02}')
 
             if show_ns:
                 ns = dts.ps // 1000
-                res += f'.{ns + dts.us * 1000:09d}'
+                res += f'.{int(ns + dts.us * 1000):09}'
             elif show_us:
-                res += f'.{dts.us:06d}'
+                res += f'.{int(dts.us):06}'
             elif show_ms:
-                res += f'.{dts.us / 1000:03d}'
+                res += f'.{int(dts.us / 1000):03}'
 
             result[i] = res
 

From 70787319e4875ad56cf7d1d27bbe8894263d7ded Mon Sep 17 00:00:00 2001
From: MomIsBestFriend <>
Date: Wed, 13 Nov 2019 23:12:55 +0200
Subject: [PATCH 4/4] Fixes to review by @jreback

---
 pandas/_libs/tslib.pyx | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/pandas/_libs/tslib.pyx b/pandas/_libs/tslib.pyx
index 08cd64c601a79..598def4e1d9fa 100644
--- a/pandas/_libs/tslib.pyx
+++ b/pandas/_libs/tslib.pyx
@@ -266,16 +266,16 @@ def format_array_from_datetime(ndarray[int64_t] values, object tz=None,
         elif basic_format:
 
             dt64_to_dtstruct(val, &dts)
-            res = (f'{dts.year}-{int(dts.month):02}-{int(dts.day):02} '
-                   f'{int(dts.hour):02}:{int(dts.min):02}:{int(dts.sec):02}')
+            res = (f'{dts.year}-{dts.month:02d}-{dts.day:02d} '
+                   f'{dts.hour:02d}:{dts.min:02d}:{dts.sec:02d}')
 
             if show_ns:
                 ns = dts.ps // 1000
-                res += f'.{int(ns + dts.us * 1000):09}'
+                res += f'.{ns + dts.us * 1000:09d}'
             elif show_us:
-                res += f'.{int(dts.us):06}'
+                res += f'.{dts.us:06d}'
             elif show_ms:
-                res += f'.{int(dts.us / 1000):03}'
+                res += f'.{dts.us // 1000:03d}'
 
             result[i] = res